Lets face it, it happens. Knowing how you body's timing works, eating right and possibly a douche before hand will help out. I just keep a package of EF wipes close at hand just in case. It has never killed the mood for me or been a problem.
It happens occasionally, no matter what you do (though pre-planning can minimize the chances). Keep some already-torn paper towels handy just in case (setting the toy on them and wrapping it up minimizes the risk of mess and any smell). You could also use a plastic bag.