[ Cats ] Open Question : A Very old cat that needs help?

Ok so there is this cat that is at my house it is very old and skiny and dirty. Its missing an eye and it seems like it has some eye incetion because dirt got into the socet or something. It has alot of good and gross stuff in its eye. What should i do? my parents say that we can't take it to the vet becaus ewe dont have money and that its going to die soon but i still want to help it. Also I ran out of tuna to feed it. I have 6 other cats and they eat regular dry food and so does sketchers (thats what we named him) but I wanna give him more wet food and protien to build him up.