It's much like having a dog , I'm guessing you have a dog as you have dog food?
Do you have any tuna or tin fish in brine maybe?
Things to look out for , like dogs ,
Worms ,
Ticks (if its been out in gardens and things there a good chance)
Fleas , young cats can die from becoming anemic from flea bites , again fleas and worms are often together ,
Lung worm , if been living in garden with slugs ,snails ,
Ear mites , black wax / dirt looking stuff inside of ears ,
A trip to vets for the once over and some kitten shots , and some Frontline, vet can also scan the cat for a chip , not likely but if its there and registered they should be able to find owner , if not put posters up in local area , supermarket , school , shop , vets , Waite a few weeks see if anyone comes foreword ,
If your not going to be letting him out for a while this will train him to retern to your house when you do let him out again then you will need a litter box and litter , litters easy to train , rub his paws in it he should use it , if not soak or pick up accident with kitchen roll and put in the box ,
Good luck with your little friend , he must have chosen you for a reason , maybe a for ever home or to help him find his ,