Sometimes in the course of answers we can misunderstand, I'll start by trying to make sure.
You mentioned that a flask was just what you were looking for, and you also said that you have an adjustable measure. Am I right so far?
I have used a small flask to load by using pouring from the flask into the measure. A small pour spout for your flask will simplify this. Mine had a 30 gr spout: its end was smaller than the opening of the measure so no funnel was needed.
Another handy choice is a small "day" horn. I have a small flat horn that carries in my hip pocket. Its small spout pours easily into a measure without a funnel. My day horn carries enough powder for 15+ charges, so it's plenty large for hunting and still be small and handy.
For practicing off a bench I have a cap for a powder can that has a spout for pouring into the measure. These can easily be made with a with a spare powder cap and a cartridge case. Again no funnel.
All of these suggestions have small enough ends to pour easily into a measure. If you want to simplify the measure, one can be made from many materials. I make a simple one by pinching the end of copper tubing and cutting the tube off at the powder level I want. I drill a hole in the flattened part to attach a cord.
The key here is what others have said: you can carry powder in many ways, but pour from it into a measure and not the barrel. If I'm headed to the squirrel woods here in a few weeks, I could grab my rifle, day horn (flask), measure, loading block, and I'm out the door. My rifle is the only thing that doesn't fit in my pocket. I could carry more, but I'm guessing that you're trying to un-complicate things.
Regards,
Pletch