Screwdriver works but be carefull. If you rip it in half it's a pain in the *ss to get off. I'd just get the cap or a strap wrench.+1
Get a long screwdriver and bang that bitch right threw the filter and use the driver as a handle and it will come right off. It gets a little messy though so make sure the oil is drained first(duh?) and make sure you have an drain can underneath.