If it's really stuck, them some channel locks and a rag probably. Sometimes it really is hard to get a good grip with just fingers. I prefer my wife's car. The oil cap has a stop and it only takes 1/4 turn.
I just loosened mine for the first time in two years of ownership as I always have the dealership change the oil. It was difficult to loosen, and I attribute it to the large tattooed brute in the service department who changes the oil. It took both hands gripping it to loosen it, and now I've retightened it, but not nearly as tight as the big brute does. It's snug, but not overly so.
I agree it's tight but not tighter than on other cars I've done. Normally I place a rag on the cap and turn with channel locks. The rag protects the plastic cap for marring from the channel lock teeth.
I changed my oil today and the drain plug and the fill cap were on very tight. I am guessing I may have put them on with a hot engine and not it is cold or who knows what. I do use a torque wrench on the drain plug so it was not tightened that hard. I actually rounded the corners on the drain plug and had to get a new one from my dealer.
I do my own plumbing and recently replaced the faucets in my bathroom and bought a handy dandy tool for getting back behind the sink. Well it turns out that it doubles as a nice stuck oil filler cap removal tool.
Personally, I think the reason it's so hard to remove is from the rubber seal on the bottom of the cap. On our car anyway, once you break this seal loose, the cap spins off easily. I wonder if you could lubricate that seal with clean engine oil, the same way an oil filter's seal is lubricated, and achieve good results.