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

https://web-wiki.win/index.php/How_Do_I_Reinforce_Cardboard_Before_Drilling_Holes_for_Handles%3F

Upgrade your reclaimed boxes and bags by adding sturdy wire handles. Use 2-3 mm galvanized wire for strength and durability. Drill 3-3.5 mm holes to thread the wire through easily without damaging your materials