Don't feed them ham, just make sure you don't run out of food! You can buy frozen blood worms from your local pet shop, buy 2 packs and put them in the freezer 'in case of emergency'.
ham is quite salty that doesn't sound good for them at all. like MrB said pick up a packet of blood worms and chuk them in the freezer they last forever
Depending on their age they can go a while without food. Even as young'uns they probably shouldn't be fed every day. Mine occasionally get bok choy and other leafy salads and love it. As said above, forget the ham and get some frozen bloodworm as back up.
It will depend on the type of turtle and its age, but most will happily eat dog/cat food, plain raw meats(chicken, freshwater fish etc.) and insects, if meat is fed often it should be supplimented with some sort of reptile supplement like wombaroo. They will also eat fish food but it probably wouldnt be good as a staple food. Bloodworms are a waste of money IMO but they will eat them. Any sort of turtle food can easily be stored in the freezer for later use. Older short necks will also eat a variety of vegetable matter.