Putting a bag on anywhere else but at home or the like where one can take (and remain) in the shower until the stoma has quit spewing and properly clean and dry around it has been quite a challenge.
I've developed a hardier (but more expensive) system of using no sting paste + a little stoma powder mixed in to hyperactivate it, as a thin coating around the stoma then covered with cut moon shaped extra large barrier strip pieces to encircle the stoma and used to press the paste down with. Doubles to cover large areas of the skin.
Then skin protectant dried on top, more paste slightly away from the stoma to marry the wafer with. Then external barrier strips (extra large and full pieces) all around attached to the wafer flange.
What this does is creates a pocket to hold output less it breaks out somehow. Thus little mess gets loose on everything else.
Most won't need something like this but my otosmy output is high and my stoma near flush in a belly fold, a most difficult situation.
Edit:
Haha, speak of the devil, just had a blowout start dripping out after I posted this. Didn't ruin the bed, made it into the bathroom and sure enough, the whole pocket was full of spew.
But to answer your question unless you have a really tame system, I don't think it's possible to get a good bag on in a gas station bathroom for instance. It's really difficult to keep the stoma clean, dry and oily free, especially if it's active.
There is a contraption online like a tube that one encases their stoma inside it while leaning on it (like against a sink) to keep it in place and collecting spew while one prepares the skin around it and slides a two piece (won't work with a one piece) wafer section over it and up to the skin with a ring or paste on it.
I thought about getting it but I have an oval stoma, not round.
Heck if round I would have gotten a piece of plastic pipe long ago.
I guess I could heat the plastic tube to be oval. 🤔
But this would only be good for a quick slap method, my efforts are more thorough due to near flush stoma and a belly fold.