You've booked your direct flight to Newark, New Jersey with Singapore Airlines. It's convenient; there are no additional transit stops to idly spend waiting for a connecting flight, nor is there the possibility of (the horror!) missing that connecting flight. But there's that caveat of spending all 18 hours rather stationary. Sure, with the Premium Economy or Business Class seats, you might be able to get a decent amount of sleep, but what you decide to wear onboard a plane, does play a part in making sure how comfortable your experience may be.
At this point, Singapore Airlines does not provide a set of pyjamas for Business Class passengers (it's an amenity only afforded to passengers travelling in First Class, which is not part of the configuration of the flight). We recommend bringing along a set of clothes to change into before the end of the flight, because spending more than 18 hours in the same set of clothes that you've dined and slept in, can be quite unbearable. And you would definitely still want to look and feel fresh despite almost not showering for almost an entire day.
With that in mind, here are four things you could do with to make your time on the world's longest flight a tad more comfortable.
Backless loafers are your best friends

Let's get this clear: no one on the plane should ever be subjected to your uncovered feet, no matter how well-maintained they may be. It's also highly unsanitary to be visiting the plane's lavatory in uncovered shoes of any kind. The best kind of shoe to wear is a pair of backless loafers. They're easy to slip off before curling into a comfortable sleeping position or stretching your legs to keep the blood flowing. And easy to slip on when it's time to disembark. Wear them with socks too, to protect your feet from the cold and to ensure you don't gross anyone out when the shoes are off.
Skip the belt

Not only do you have to take it off (and then put it on again) before going through the security scanner, sleeping with one can be quite restricting. Add to that the seatbelt that you should always have on while seated on the plane, you could do without the former. Trade your belt-looped trousers for more streamlined trousers that are designed with side adjusters, for a snug fit without the need for a belt. Or a pair of tailored drawstring trousers in a formal enough material that you won't look sloppy in.
Keep warm always

We're quite certain we don't have to tell you how cold it can get on the plane. The provided blanket is nice but is hardly sufficient to keep you comfortably warm throughout the flight. Even if its summer in Newark, your best bet is to turn up for the flight in a plush cotton hoodie; a boon if your head tends to get cold too. It's not necessary to pile on the layers, but having the option to remove your hoodie if it gets somewhat stuffy, and then using it as an extra pillow (or something to hug to sleep) is always a plus.
A proper cotton T-shirt or shirt

Spills and small messes are quite a natural occurrence, especially when turbulent weather hits. If you've got your hoodie on, you're safe. All you need to do is take that off and it's as though nothing happened. Which means, never forget to wear a proper T-shirt or a shirt under your hoodie. And by 'proper', we mean, not an undershirt. Get a cotton crew-neck T-shirt instead that you can pair with a jacket once it's almost time for landing. If you don't want the added weight of an entirely new set of outfit in your hand luggage, this will at least ensure that an extra jacket is all that's required.