Pads of forms they can use to get their sexual partner to sign off on consent. It would take the ambiguity out of situations like:
1. Oh, s/he has had half a beer - s/he might turn around tomorrow and say the sex we had was non-consentual.
2. s/he hopped into bed after I bought dinner but when I didn't buy breakfast s/he is calling it rape.
3. S/he said s/he wanted to be tied up and post a video online but after the fact is having second thoughts and saying it wasn't agreed to..
The list can go on... but if you just had a pad of sequentially numbered three copy carbon forms outlining the agreed upon details of the rendez vous, signatures of both parties, a copy for each partner + an original for file records you could avoid a whole lot of messiness. For added protection, you could always get the form notorized.
The added benefit of which would be if when filling out said form you notice "oh, I'm form number 000525" then you can double wrap it. Or, clubs could have contests where you bring in your completed office copies to enter them in a draw for a free drink! Imagine the possibilities! —This is getting too much....