I tend to get at the supermarket a packet of stir fry vegetables but sometimes find they have too much cabbage in them.
vegetables you tend to find in them are: -
beansprouts, sugar snap peas, baby sweetcorns, red and/or green peppers, onions, sping onions, pack choi, carrotts, sweetcorn (ordinary) and water chestnuts (which you can also get in tins).
I would say basically you can use any vegetables you like, I tend to find its the sauces you use that make the difference. I also like to cook mine a person a time ie I will cook a portion for one person then do a portion for another person after that as they don't take long and cook better with less in the wok. This also means you can put in what each person wants each time so no one has to pick out the bits they don't like.
I have also recently discovered some cooking oil especially for the wok I can't remember if it was wok oil or stir fry oil but it works much better than olive oil which is what I was using before.