I won't try any of the non-kosher fishes, meats, or poultry sources. Anything else is fair game.
There are many neutrals (and diamonds and beneficials for that matter) that I haven't yet tried, either because they're not available near me, or they're just WAY too expensive when I do find them. If it doesn't grow near me, it's not going to be affordable.
There are also a few meats that are theoretically kosher, but hard to find with a reliable kosher symbol, or are WAY too expensive when I do locate them. For example, I've never eaten venison, buffalo, or mutton. Lamb is very expensive, so I only have it a couple of times a year. I've found kosher veal, but I have an ethical problem with how it's raised, so that's one meat I won't buy.