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

https://wiki-club.win/index.php/What_Hole_Size_Should_I_Drill_for_2-3_mm_Wire_Handles%3F

Upgrade your reclaimed boxes and bags by adding sturdy wire handles. Use 2-3 mm galvanized wire for durability and thread it through 3-3.5 mm holes for a snug fit