Variety of cheeses and crackers and/or nice bread. Cheeses can go in a mini cooler / lunch cooler pretty well, and the crackers / bread don't need much care.

Cut fruit is easy and keeps well enough for a few hours.

Corn bread is always yummy hot or cold.

Grab a bagged salad and some dressing on the way to work toss in a bowl before the potluck starts, there's almost never enough vegetables at potlucks. I suppose getting a pre-cut veggie platter would also work, you can throw the dip into a small lunch cooler with an ice pack until the potluck.