The cheapest thing on this page and the one that decides whether any of the rest of it works.
Decanting solves several storage problems at once and creates exactly one: the date and the contents were on the packaging you threw away. A cupboard of identical unlabelled containers cannot be rotated, because first in, first out requires knowing which one came first. What happens instead is that the front container gets used repeatedly and something at the back quietly ages out.
Write two things: what it is, and the date on the packet it came from. Not the date you decanted it. The best before date belongs to the food, and copying it across is the only way the figure survives the transfer.
Practical notes. Permanent marker on a smooth container is not permanent once it is handled, so use a label rather than writing on the plastic. Freezer labels release cleanly when you reuse the container, which ordinary address labels do not. A roll of masking tape and a marker is the field version and works fine.
For anything going into Mylar, label the outside of the bucket as well. The bag is inside a sealed container, which means checking it requires opening the thing you sealed.