Mylar bags are great for placing inside 5 gallon buckets if you are unsure if they are food grade or not. You can also use them inside metal garbage cans if you are storing food someplace where rats might chew through plastic. You need to seal the bags first to ensure the food inside stays good for the longest time possible.
There are two very easy ways to seal these mylar food bags. The old standby way is to use an iron. But a much easier way is to use a hair straightener. You can purchase them fairly inexpensively at WalMart etc. If you are worried about the mylar melting, you can use a couple layers of paper towels to act as a buffer between the two.
Before sealing, always check for any bug contamination, even if you only kept it in the garage for a few days before sealing. You don’t want to discover upon unsealing it in an emergency situation that it has been contaminated with creepy crawlies.