I debated long and hard before deciding to add my answer to this challenging call for a satisfying lifehack eschewing the use of any apparatus beyond one's essential corporeal being.
I sincerely feel that the only proper way to finish a bag of finger food when you're munching with your fingers is to… (wait for it)… use your fingers; but, technique is key (yet again) to success.
When you pull your finger from the container after tactile feedback confirms only crumbs remain, and visual inspection validates this, remove the material from your appendage(s) by placing it/them in your mouth directly and suck the material from it/them until satisfied with your efforts at success.
Avoid any extraneous movement that might dislodge larger particles that might be tenuously held from failing oral insertion en-route.
Select a finger as your choice and re-insert it still damp from the saliva in your mouth to the container bottom. More crumbs will stick to it. Retrieve your finger from the container and place it into your mouth and repeat the lingual extraction of the material from your finger.
Repeat this behaviour until the desired amount of material has been withdrawn.
And, as always, I wish you Good luck.