You say it's hand luggage only. Therefore presumably a short trip. If you really need your protein supplements during your one business meeting or whatever, could you not do what everyone else I know does and manage on protein bars? Far more practical and less like to spill than a plastic bag. I know they work out more expensive, but for a couple of days make far more sense, no? And if kept in their wrapping unopened you wouldn't even get questions at Miami or Tel Aviv, let alone Dublin!