What should I pack for vacation?

what should I bring when going on vacation?

Well ideally it really depends on where you are going - what you are doing - what the weather is looking like when you get there.

Ideally the important must haves for any packing is going to be -
clothes
toiletries (toothbrush, shampoo - for this I always just get a couple of mini bottles - etc)
a book or something for along the way - especially if I am not driving
snacks
water

but the bulk of everything really depends on other variables - where are you going?