Like all things, just keep offering till they accept it. It often takes quite a few goes before they'll eat some things. And then they'll love it one week and then refuse it the next.
On bickies and things I'd just suggest avoiding very sweet or salty things. They don't need the seasoning and you just end up giving them a taste for it. We gave DS lots of rice and corn cakes as snacks, as they're pretty much just rice or corn.
Instant noodles are one of DS' favourites. Oh, we tried to keep him on natural, whoel foods when he was little... well that sure did go out the window.