I buy protein bars for travel - I buy whichever is lowest in carbs for the total protein - Quest is my current go-to bar. I also avoid those that melt and get messy, which are also usually higher in carbs anyway. Can keep one with you on a plane, use for breakfast in your room if you go to the hotel gym early, etc.

If you insist on powder how about buying it in packets? I use Labrada Lean Body Protein packets at the office - allows me to carry it around with no chance of spillage. There's a number of brands that come in packets - it usually costs more per gram but would be convenient and solve the TSA problem. Again I look for the lowest in carbs, but I'm not bulking (not now...)