For the better solution, if you do enough potlucks, or even if you don't, but you need to get a baking dish, Pyrex has a line called 'Pyrex to Go' which come with a tight fitting lid, an insulated carrier, hot & cold packs.
For those times when I'll need to hold things for even longer, I'll put the whole thing (insulated container and all), into a soft-sided insulated cooler that I have that it just barely fits into. (and if I'm really paranoid, I pack the bottom w/ towels, and more on top for extra insulation).
Now, all of that being said .... the easiest way to handle these sorts of things are:
- Plan a dish that doesn't need be served warm.
- Find if there's some office that has an oven, hot plate, or microwave, and select container as appropriate. (strangely, I've actually worked in a place where there was an full stove w/ oven a couple floors above me, in where the executives had their offices ... why, I have no idea.)
- Select containers with a good thermal density (in this case, the cast iron is great)
- Select containers with a low surface to volume. (ie, more 'squat', not tall & skinny or low & thin)
- Use heat packs ... something else to store & retain heat. (the reusable ones if you can, not the ones for emergency kits)
- Ask your boss in advance if you can come in late ... your missing an hour or two of work is better than 1/2 the staff getting food poisoning.
If you're going to have electricity wherever you're storing it, consider a slow clooker / crock pot ... or, wrap the whole thing in an electric heating pad until serving.
If it's going to be in a well supervised place, the next alternative is a chafing disk that uses either sterno, or tea candles. They make electric ones, but I'd rather go with the heating pad, myself. (under a tray, so stuff doesn't drip on it)
And one problem with all of these solutions, except for finding an oven ... your food's going to steam the whole time as you'll have a covered container, which might not be all that great for a hash. And most places might look at you strangely if you brought in a blowtorch to dry out the top.