Yup, I do! Honestly...you probably shouldn't be.
But on the other hand, Patty would probably love the extra help to make it through winter, and it's not a HUGE deal. I know you're smart enough not to get too up close & friendly with Pat or any other critters! The biggest risk is acclimation to humans, which isn't safe for any wildlife.
Cat food is just fine. Honestly, we use the cheap crap for our staple for opossums at the rehab I work at, with kind of whatever we have donated thrown in. They do fine on it - it's mostly for something to keep in there that they can munch on whenever they want along with a general source of nutrients. Their main food is whole mice, along with fruit and yogurt. I've tried giving them Chop (minced veggies) before and they won't touch it.
You can give whatever cat food you want, really. As far as I know, the protein & such doesn't matter (our assistant director gave an old education opossum dry Evo food, if I remember right, when he first came to us with severe nutritional deficiencies), and higher fat will probably be a help to deal with winter weather. And depending on your preferences, higher quality cat food would probably be better.
Keep in mind that while opossums have a home range, it's relatively large (11 acres or so) & they'll be nomadic over that range, so there's a chance he/she won't stick around. But they probably will with a steady food source, especially with the cold coming. You might also start seeing Pat more during the daytime as it gets colder. They're generally nocturnal, but opossums are really not built for cold, so when winter comes around, they'll be out more during the day when it's warmer. They do have a tough time in the winter because of how little food there is available to them. Because they're not designed for below-freezing temperatures, they also frequently get frostbite on their ears & tail.
We often get opossums in the winter that are feather-light from not enough food & have wounds from the frostbite. A lot of times they're our own babies that decided to come back to the hotel.
Few weeks & they get fat & sassy again, and then they're rather unpleasant guests until spring! I always told them it was their own choice to come back, they should be grateful to get regular meals again.
Also, just a forewarning, you may get more visitors than you bargained on with the cat food - raccoons love cat food too & will happily take free hand-outs. Unlike opossums, raccoons will happily move in if there's an inviting spot, so be careful if you have a garage, shed, etc. that might look like a cozy spot for a den. And while it won't be a problem for you as much with no cats/dogs, a warning for others that raccoons carry raccoon roundworm, which can infect all other mammals & can cause major tissue damage, or even death. The eggs are not killed by freezing temperatures, only high temperatures (think boiling water or fire). So that's a concern to keep in mind if you have raccoons around! They also carry more diseases than opossums, including rabies. Opossums can't carry rabies - being marsupials rather than placental mammals, they have a lower body temperature, too low for the rabies virus to thrive.
But yeah, just be warned if you do end up with raccoons around. They definitely have their charms, but they do have some major drawbacks & they're usually much nastier. Opossums are generally all bluff - they don't see well & are easily startled, and they open that mouth to show off all the scary teeth they don't really want to use.
I'd rather deal with an unhappy opossum over an unhappy raccoon ANY day!
But heh, I'll stop now. Sorry if you got more than you bargained for, I like talking about wildlife too much. Or about any animals!