Sardines and mackerel - nice snack on toast, especially with a good squeeze of lemon before serving. Toast bread one side only under the grill, put fish on the untoasted side, grill till just heated through, serve immediately.
Otherwise, mash up with cottage/cream/curd cheese, some lemon juice, maybe a little chopped parsley, to make a simple pate.
Tuna - sandwiches. Mix with mayo, add sliced cucumber. Or make a simple chilli-type thing - fry an onion, some garlic, mushrooms, a green pepper, add a chili or cayenne or chilli flakes or hot paprika, maybe a little ground cumin and/or coriander as well, tin of tomatoes, some tomato puree, a tin of red kidney beans (drained) and right at the end the tin of tuna (also drained), plus some lemon juice. If it's tinned in oil, I use the oil to fry the onion etc at the start.
I like tinned ham, but it's an acquired taste. I'd have it in sandwiches or with salad, jacket potatoes etc. I particularly like the jelly, which is what puts a lot of people off. 
Tinned chicken - in sauce? Vol au vents?