Plastic buckles, particularly those found on backpacks, can take a beating as they get banged, dragged and scratched through the outdoors. When they inevitably break, a repair is relatively simple with the right spares.
A buckle with Buckley's...
Create a loop with a Slick Clip
Screw in a pin to hold it
Et voila! Solid as a rock
The first step in replacing a buckle is to pick up an appropriately sized replacement. Sea to Summit manufactures a clever Field Repair Buckle with removable pins which attach through loops in straps. If you are fortunate enough to have broken a buckle which is attached to pre-sewn loops, just break off the old buckle with pliers, then attach the replacement by removing the pins and inserting them back through the loops. Unfortunately, not all packs have pre-sewn loops at the end of the strap. If this is the case, a nifty gadget called a Slick Clip (or a Quick Attach Tri Glide) can be used to create a loop in the webbing. With this in place, the replacement buckle can easily be fitted.
Tip: a pocket knife in your trail repair kit comes in handy with this repair and many others. Make sure you pack one.
Sea to Summit Field Repair Buckle: $5-6 depending on size
Slick Clip: approx. $2