Snack mix like Chex mix I cook, directions on chex mix package, easy to do in the microwave but then I like to bake if for a while, it makes it crunchier. I put in other cereals like Cheerios, Crispix - basically any nonsweetened ones. I also put in nuts of any type esp salted peanuts. Small pretzels or pretzels stick, small bagel chips etc. are also good. I guess you could put in M&M's if you wanted some taste variety but not until its cooked/baked and cool, then throw them in and toss it well.
I don't put dried fruit in it, that to me is in trail mix which is not cooked, but its great to make up a batch of that to take with you too. I have gone in the hottest months of the year and had no trouble making it with M&M's - they don't melt. There are lots of recipes for trailmix.