Upgrade your reclaimed boxes and bags by adding sturdy wire handles. Use 2-3 mm...

https://fun-wiki.win/index.php/Cardboard_Sandwich_Method_for_Bag_Handles:_How_Do_I_Hide_the_Anchor%3F

Upgrade your reclaimed boxes and bags by adding sturdy wire handles. Use 2-3 mm galvanized wire for strength and drill 3-3.5 mm holes to thread the wire through cleanly