Depends what sort of session you have planned. Obviously a bath tub is easy to clean. would also recommend a good sized paddling pool. Shaving foam is easy to use but can burn the skin depending n the person. In Britain Angel Delight etc makes good pies with good coverage that are easy to make and quick to clean up. Generally I find custard too cold and watery for pies but as a gunge it looks good and is easy to clean up. ideally you want something not too bad for the hair either, so custard and angel delight work in that respect. Would avoid whipped cream. It looks okayish but leaves a lingering smell.
Just going on experience. yet to find the perfect recipe but that's what we have found.
Use a dustpan and shower squeegee to get the mess up and then flush it down the loo. The squeegee makes very easy wotk of getting it off the bath and tiles and even yourself and they are super cheap
A small kiddie pool works well for solo action, although it can also work for two people, if you're careful. The great thing about the pool is that you can scoop out most of the gunge, toss it wherever, then deflate the pool and toss it out. Of course, a shower/bath also is good.
Give me treacle anytime, although it's pricier here in the States. Fortunately a case can be ordered through Amazon.