if you bought a grease cartridge and dont want to load it into a gun then simply cut the cartridge and empty all of the grease into a container (e.g. old baby cereal container) or any other container of choice - make sure it has a lid. I sometimes buy grease in bulk clearance and need some in a small jar, I use a washer and long rod in the cartridge top, pop out the metal cap, push the grease out into a container and job is done.
My most used grease gun always have valvoline durablend grease (still have like 20 tubes left in carton), I really like it for greasable ball joints and tie rods.
my wheel bearing stuff is also bought in cartridges but I empty them into containers or just spoon them out - for CVJ grease I use the bag again - spoon out 100 grams of it, and use it like an icing cone.