I've done some in the past, and hoping to do more soon with my fiancee. Honestly, anything cake batter, pies, pudding...you can do just about anything as long as the substance wouldn't burn your dirt road, lol.
Funny you should ask! We are considering another session.
My partner purchased a harness and a set of 3 dildos named "strap u tri-play" (small, medium and large). I did some considerable prep in the shower leading up to the night. But it's an intense and intimate feeling when the time comes, and preparing wont do it justice.
Use a water based lube! Communication is also A BIG part of the process.... unless you cant talk.