I use a glass generic Rubbermaid container. Has held up well for a few years now despite sitting on the bottom of my backpack which is banged around at times. A glass lunch container seriously isn't that heavy, and it cleans up nicely. I sometimes forget about it over the weekend; a quick soap down and it's ready to go Monday morning.

Cold goods get kept in a fridge/freezer in the staff lounge. Housekeeping doesn't have access to it and said staff is small so no stealing thus far.