Well, I'm not sure for 16 y.o.'s, but some things I'd consider:
- in addition to crepe paper vines, you can buy big bags of rubber snakes, insects, spiders etc. at the dollar store or toy store, and use them for decorating - if you are doing loot bags, everyone can take some home
- cheap straw hats and bandanas for everyone to wear and get into the fun - again to take home at the end of the party.
- I like the jungle juice idea - I'd look for jungle food ideas, if you google "jungle birthday party food" a lot of links pop up
- music - some hokey old tunes like "The Lion Sleeps Tonight", "Jungle Fever" etc.