I have the exact same bag that thew OP describes, and it works fine for me. I carry a complete change of clothes and when carrying food, it keeps the contents warm for at least 45 minutes. The only issue is that when fully loaded it tends to be somewhat top heavy. But nothing that can't be compensated for.

Well, exactly what is the problem with just stuffing your lunch into your backpack or panniers? This is all I do.

For example: If you make your sandwiches with bagels, they won't get hoplessly crushed. You won't wind up with a peanut butter and sponge filled with jelly sandwich.

I do give bananas special attention, though, through careful packing. I hate banana bruises!

From the original post:

"Before I just had tuperware containers in a plastic grocery bag, inside a backpack and got mixed results with stuff, spilling, etc."

Tupperwear and a backpack is about the most efficient way to bring a lunch. Closed properly, tupperwear doesn't leak.

If your simply looking for a change or something different, that's......different.

I just use a disposable (which I don't dispose) "tupperwear" container and bring stuff that isn't soup, usually rice and stirfry. I use a plastic grocery bag for insurance against leaks. I just bring the main course; snacks like apples, etc. are kept at work.

I use one of the Topeak MTX bags and it does the trick on my 16 mile commute. I took the brackets off of the bottom and I just use the velcro staps to attach it to my rack.