Alcohol based hand sanitizer (Purell is a popular brand) works extremely well in a Trangia, boiling a small pot of water is about four minutes. I'll bet your office has some handy; if not, it is extremely innocuous.

Sterno is worthless for cooking, but OK for warming. You could probably make a decent alcohol stove out of a Sterno can.

Also, an empty Purell bottle makes a fine container for liquid alcohol if you want fuel that has a higher heat content.