Tim, don't sweat it. Almost everyone who does muzzleloading has a flask . I have a flask but I just don't use it anymore. Actually I have two flasks. One I made from wood with a carving of a 8 point whitetail on it.

A 1 lb canister can serve as a means of pouring into your measure with one of those funnel caps I previously mentioned. In that sense they turn your canister into a flask for use at home (pre-measuring vials) or at the range. Of course that wouldn't work well on a hunt if you weren't carrying pre-measured charges and need to measure a charge. That's the circumstance where a flask is handy to have.

I pretty much do what you are planning to do. I pre-measure my charges and put them in the vials prior to going to the field or the range. I use the canisters with an appropriate spout to pour the powder into the measure. But using the flask is pretty much like the oldtimers did it. Its good to experience that so don't fret the flask.