For men, DO NOT, I repeat DO NOT wear a formal white dinner jacket. I don't care what its called, its just not practical (for one, see the above sauce warning)! And besides, its out of place unless you're attending a dinner party on a yacht (like P Diddy does here in 2008 for Roberto Cavalli's annual Cannes Yacht Party - he's pictured with the host because he knows the rules);
attending a dinner party at the home of someone in the original Rat Pack; attending a dinner party in some European consulate; attending a dinner party in the White House; attending a dinner party on the set of the AMC show Mad Men (these people followed that rule - but then again, they're the actors);
attending a dinner party in the 1950s; attending a dinner party and you are LITERALLY James Bond (the British spy, not some chump who just lucked into that name - as Sean Connery and Roger Moore, respectively, did when they were themselves that man).
Now, for the single utensil, there are four aspects which need to be taken into consideration. Because of the (probable) occasion and level of formality called for, you first have to consider the potential elegance of the object (30% of equation). Portability (22%), practicality (22%), and versatility (26%) are the other necessary considerations.
Now, depending on your age, dexterity, origin, favorite foods and place of residence, your thoughts might first jump to taking Choplery (as pictured below).
I mean, sure, a set of chopsticks is technically a single utensil no matter whether they're married with the amenities of 'Western' cutlery. They can be considered highly portable if they're not too big to fit the inside breast pocket of a men's jacket or a woman's clutch/handbag. They can be elegant if of a high quality, non-toxic-coated wood product or done in a stainless steel mirror finish. And if you chose the cutting Choplery, you can takle the issue of larger-than-bite-size food items. But its not completely practicle. What if there is a soup corse (no doubt there will be)? What if the desert is a custard or a mousse, perhaps a sorbet or an ice cream (this is a formal dinner, not a 7-year old's birthday party). So, the Choplery loses partially on practicality and almost wholly on versatility.
The best multiple-capability utensil must be uni-, not bi-directional to truly be formal-party-appropriate. The importance of keeping food off your person cannot be understated - a bi-directional utensil always presents the danger of having an end with messy foodstuff too close to a diner's person and certainly too close to a gentleman's cuff. So this brings us to the mealtime multi-tasker so many of us were introduced to as children - the spork.
Now, there's two prominent versions of the spork. There's the utility (or camping) spork:
And common spork incarnation #2 is the flimsy piece of plasticware so many of us know so well:
Boys and Girls Club back home. They came in packets just like the one pictured here. Except I remember ours having little salt and pepper. Hopefully Im remembering wrong because those lunches consisted of a fruit punch/juice, a (usually soggy) bologna or ham sandwich, a bag of chips, and a (usually frozen) fruit cup. Sometimes we'd put the chips in the sandwich just so it would have some mouthfeel and non-wet bread texture. The thing about these sporks, though, was that they SUCKED. You'd use their spikey end to pop through the plastic seal of the fruit cup. But if you didnt utilize it at the right angle, the handle portion would bend or the spikes would simply not penetrate the thin plastic seal and just bounce off.
As I think I've illustrated, a spork simply cannot be elegant enough for this fancy dinner party. Besides, there's no good way to cut with a spork, making it weak in the categories of practicality and versatility.
To tackle this conundrum I did a bit of trans-continental research and (from a sampling**) found that (statistically speaking) a staggering one out of two Englishmen - when asked what they would chose were they only allowed use of a single utensil - would use a soup spoon. A soup spoon! For a whole meal! Really, no wonder they  lost The Revolution to a bunch of ragtag, but ultimately heroic, settlers;  still revere their royalty and pay for their extravagances even though said royalty has no real political power; and  democratically elected the now derided Gordon Brown to be their leader (retrospectively speaking, maybe they aren't so ready to be without a ruling monarch). Here is the documentation of the sampling**:
The other half of the sampling had an answer that bellied the grit and intelligence of what made Britain so good at Empire (when it was en vogue). This half knew you needed the basic abilities and ideas that make the spork, but you need a utensil with more class and more cojones. This half chose THE SPLAYD!
As you can see, the Splayd is effortlessly elegant. And if you understood its history, you'd understand why the Brits would know so much about this eating device. It was made in the mid- to late-60s and comes from Australia - making it one of the coolest things to come from the land down under along with pre-Wolverine Hugh Jackman, boomerangs, and Outback Steakhouse. It takes the idea of a spork (as illustrated in the below diagram from this blog post),
Since this is obviously a gorgeous piece of design and is just as portable as any fork or spoon, the Splayd receives perfect marks in the categories of elegance and portability. But just as there are inevitable shortcomings in the design and building of multi-use spaces, there are slight shortcomings in this multi-use utensil. As they say, it can be designed perfectly for a single use or imperfectly for multiple uses. And according a review of the Splayd (the outcomes are graphically resented here)
it receives pretty good marks for versatility, but gets a not quite stellar mark for practicality. Though its good for many things, the Splayd is not quite great for enough to make this world single-utensiled (thoug it is your best choice for this dinner party). You might have to ask your table neighboor if you could use their Choplery or soup spoons when they're done with them. But a man in a tuxedo or a woman in a dinner dress can often get anything they ask for (just watch the previously mentioned James Bond movie series).
To sum up this essay-length blog post (you're welcome, person who told me I should write longer posts), the Splayd might be good enough to be the only utensil most people need for most of their meals, there's just some foods that a Splayd can't handle. I have, however, been inspired to want to host a Splayd dinner party one day. It may or may not be a (semi-)formal event and the menu is a work in progress. At least that'll ensure another blog post!
**Source of Sampling:
The Bugle: Audio Newspaper for a Visual World
Issue 93 - Oil is Running Out, Bring on the New Stone Age!
By Andy Zaltzman, John Oliver, Tom Wright
From Times Online, October 16, 2009
< http://www.timesonline.co.uk/tol/news/world/us_and_americas/us_elections/the_bugle/article6878690.ece#cid=OTC-RSS&attr=6273788 >