If you've got one of the old school traps I'd also make sure you have a blunt instrument, like a shovel, too. I say this because in my experience with mice the traps often don't kill them, so you may come down in the morning to find a badly injured but not dead rodent and you'll need something to administer the last rights. It's not pleasant and it sucks that this has happened to you but you can sort it given time and a methodical approach.
Also, don't use poison. Apart from the obvious risks of accidental contamination, if your trespasser does eat some, he or she will crawl somewhere inaccessible to die and that will not smell good. Had a friend who made that mistake. :(
Good luck.