No worries --- we'll help you deal with these pests without having to rip out your plants.
For slugs and snails I'd use a slug/snail bait; you should be able to find them sold under a variety of brand names, including some that are organic. Simply apply them according to the directions on the packaging and that should help cut down on the slugs/snails.
As far as caterpillars go, if they're large enough, the safest and least expensive way to deal with them is to drop them into a bucket of soapy water. If that's not an option for you, you can also look for neem oil at your local garden center; this should take care of the caterpillars, as well.
I hope this helps. Good luck!
Senior Garden Editor, BHG.com