As a photography teacher, I am not a big fan of disposables. I miss my zoom lens and the other bells and whistles. Still, I have to admit that disposables have their place -- and the beach is one of them! Here's my advice on making the most of your disposable camera:
1. Don't buy the cheapest disposables -- they're not all made alike. Get the ones with the slightly better lenses. Look at the boxes -- you'll be able to tell which are which. In general I prefer Fuji film (better colors, studies show it's more long-lasting), but I think Kodak has cornered the market on quality disposables. I dislike Fuji's underwater cameras because of the awkward shutter release button.
2. Plan to use disposables outdoors only. Indoors you're just wasting your time.
3. Have your disposables developed immediately. This is good advice with any film, but it's particularly important with disposables.
4. Black and white pictures taken with a disposable will be C-41 instead of true black and white. Actually, most black and white film (disposable or non-disposable) is C-41 -- it's B&W film that can be developed on color paper. Considered quite a break-through in the photography world, it's the reason we're all so ga-ga over B&W photography now -- it's made B&W photography available to the masses. Your pictures will come back with a "soft" look; you'll have shades of grays in addition to the black and white. This type of film can be developed at any drug store and is inexpensive to develop.
In contrast, true old-fashioned, professional B&W film is more "crisp" looking -- the blacks are black and the whites are white -- these are the really striking pictures that we admire in photography books. You aren't going to get that stunning look with C-41 film. Most developing places can't develop true B&W on-site, but instead send it out; thus, it takes about a week and costs about $20/roll for developing. To the best of my knowledge, true B&W film isn't available in disposables.