I've actually had reasonable success w/ biscuits and muffins in toaster ovens.
My old garage sale toaster oven was perfect (and, FWIW, a 'jiffy mix' makes 6 large muffins. a 6 hole muffin pan just *BARELY* fits into a standard toaster oven. Ta-da )
I've got a good sized toaster oven (burners on top and bottom, temperature controlled) and I've done muffins, biscuits, cookies (including Christmas cookies), moist cakes (like banana bread), bread pudding, apple crumble, baked custards, tarts, homemade granola, and cheesecake. Cakes in general don't work well (heating element is too close, heat is too uneven), and full sized pies are a bit tricky to cook evenly.
I've also done fish, chicken wings, baked chicken pieces, small casseroles, braised meats, small roasts whole duck, and a Christmas turkey.
For biscuits - the tricky part with a frying pan is that the heat is much more direct and much more intense than that in an oven, so it's easy to burn things, or for the outside to be crispy while the inside is still raw.
If you're talking biscuits in the butter cut into the flour, baking powder raised, eat with gravy or butter style, look for Welsh cake recipes, which are intended to be cooked on a griddle. You need to make fairly thin biscuits here, and I think a heavy iron frying pan is essential.
If you're talking cookies (creaming butter and sugar, sweet), then I would only try it with a dough that was fairly stiff and needed to be rolled out fairly thinly, rather than stickier dough that's dropped onto the pan. The stickier doughs I think would be a real mess, and would melt, burn and stick to the pan. For the firmer doughs, I'd try a heavy pan and not too high heat, and you may need some butter or oil to keep it from sticking.