Accessories
it's no good to have a horn unless you have the all the doo dads that go along with it to keep it in shape. what is necessary? what is not necessary? i'll try to answer these questions...
i hope this is painfully obvious, but the most important accessory is the mouthpiece. for tuba, i use a conn helleberg. it's simply the best overall. bach does make perfectly accebtable mouthpieces, but they are bulkier than the conns. they are good perhaps for a beginner but before too long, i recommend the switch to the lightweight, practical, freeblowing C-H. if it's good enough for arnold jacobs, it's good enough for me.
for trombone and euph, i use bach 6 1/2 AL. it's pretty standard. it offers a much darker sound than that icky 12C. another good mouthpiece, though, that i like is the denis wick. of course that's awful vague. dennis wick makes a gajillion mouthpieces and cups, rims, and shanks. but from everything i've tried and heard about them, they are good quality ... when buying a mouthpiece, ask if you can sample the different kinds. be sure to you know whether to get small or large bore, depending on the individual instrument.
also very important is the case. bone and euph don't usually consider this when buying, becuse the case is a pretty standard feature. many players though will discover that they want a more lightweight means of toting that hunk of brass around, and then look for a nice sturdy gig bag.
tubas come with nasty hideous bulky cases that could easily store a murdered body. (please do not ask how i came up with that comparison; it's best not to know. please don' ask.) other than this morbid purpose, they aren't good for anything. that's my opinion anyway. it costs a pretty penny, but look into investing in a large gig bag. it's much lighter and more transportable.
trombones will often see the need for a mute. there are myriad different mutes on the market. you need two basic ones to function: a cup mute and a straight mute. metal mutes are usually the best, but don't go spending a fortune on mutes unless you're some sort of jazz freak who does gigs all the time. (a trombonist with a lot of gigs? uh huh.)
trombones will want a stand, so that they can set their horn down on something other than a chair, which is a recipe for disaster. tubas, buy one of those neato little thingies that you can rest your tuba on while you play; this way you don't have to crane your next and thus restrict air flow.
three accessories that i find very helpful, not only for low brass but any musical person, are the metronome, the tuner, and the music stand. work with a metronome every time you play; it will greatly improve your sense of time, beat, and rhythm. use the tuner to tune individual notes. this improves your sense of hearing, and also makes everything you play in tune. that makes you a better sounding musician in general. it also helps you discover the peculiarities of your horn. the music stand, obviously, is a convenient place to rest your music while you play it. duh.
other stuff: tubas and euphs want valve oil. cool bones will use slide cream, and loser trombones will want slide oil. get a polishing cloth and furniture polish to make your horn pretty. buy a snake. makes sure you have extra cork around in case your spit valve ever messes up. trombones, get a cleaning rod. to learn how to use this stuff, go here.