The yanks are always 'canning" stuff, like wort, in glass jars that are then water bath processed.
I buy a kilo of light extract and use that to make starters, but might start doing what one brewrat does: on his brewdays, after he has sparge the volume he wants, he sparges a litre or two extra, pours it into icecube trays and freezes it. Microwave a couple if wortcubes, voila, instant starter!
Stay away from the homebrand stuff: probably has lots of unmalted barley syrups, and your yeast does best on maltose
Jovial Monk