I have some possible production sound work coming up where I would be booming. What type of clothes would be the best to wear? Baggy clothes? Tight clothes? I vaguely remember going over something like that in a class back in college, but I can't remember what was suggested.
Wear whatever you feel comfortable in. I wear simple darker tan cargo pants with medium sized pockets on the sides of the legs (Left side pocket for holding my sides [small copies of script for the days scenes], Right side for trash [gum wrappers, used gaff/paper tape, dead batteries]), black heavy duty t-shirts (short and long sleeves; Carhart's never wear out), and very comfortable rugged shoes (I wear very comfortable climbing shoes that have a non squeak sole that lasts forever).
I also have a utility belt setup with my leatherman/flashlight/scissors/pen holder (small non-stick scissors [usually for cutting topstick, or making small holes inside pocket liners for hiding transmitters], blue push button ball point pen, black & red fine point sharpie [for making notes on the sides]), two small camera pouches for 9v & AA batteries (sometimes your utility sound guy is busy off set and you need new batteries in a pinch for actors wires, or your wireless boom), small headlamp case for my petzl Tikka, small neoprene water bottle case, medium sized utility case (holds sunglasses, quick battery tester, Rycote under & over covers, & a Lectrosonics SM Remote), plus a rock climbers chalk bag (for holding the excess cable from an internally cabled 20 foot boom pole). I roll the extra cable into a small 3 & 1/2 inch "over/under" coil leaving the the side attached to the transmitter (clipped to the utility belt) close to my body and the side leading to the pole away from my body on the opposite side of the bag so I can easily pull more cable free if the pole needs to be lengthened quickly. Also, the chalk bag is centered at the front of my belt so I can easily switch the direction of the boom pole in my hands, depending upon the direction I need to stand to accommodate the camera crew (you always want to face the camera; it's always good practice to see what the camera is doing as you boom a scene, plus camera may need to motion to you for a quick change during a move and you don't want to miss their lead). The utility belt also carries my IFB feed from the sound mixer (so he can tell me when my work sucks; in private).
I also wear Jersey gloves, the dark brown work glove you buy at home depot for a dollar a pair (6 bucks for a pack of 6; one pair last between 1 - 2 months). These gloves allow me to slide the pole effortlessly and quietly (twisting back & forth/up & down my guide hand [the hand that holds the weight of the pole]) for scenes with fast cues, and they also keep my hands clean for moments when I have to quickly work on an actors wire. Another good thing to do is have the cable from your headphones routed through your shirt. It's uncomfortable at first, but the payoff is that you never get caught on things or other crew members radios as you move during a scene or when you have to run on set for an unexpected "Roll Sound", while you're eating cheetos at craft service.
I've been booming with this setup for a few years, detailing it as I go, and it's worked great. I like to be a little over prepared; I'd rather have it and not need it than need it and not have it.
Good luck, And have fun making sound for movies,
Natural fibres, dark colours and no logos. Your clothes should be silent and you shouldn't have anything in your pockets that can make a noise either. If you come too close to a light source you don't want any of it to bounce off you. A funny t-shirt or distinctive logo can be distracting to an actor, keep everything plain. On set you should blend into the background.
I like baggy pants, because they usually have bigger pockets, but the're no good if "whispy" or rustly, then i would go with tight pants and utility belt. (they also go better with long-johns if its cold). Dressing dark may help avoiding reflections showing up in windows etc. And bring out the comfy shoes of course, and most definitely gloves if its cold.