Choose a Combination or Padlock Using an Aluminum Can and Box Cutter
Most consumer grade locks are not as reliable . That is, if you ever need to open a simple keyless padlock or combination lock, all you need is a can of soda, a paper cutter, and some precision cutting.
As shown in the video above from Howcast, you can (carefully!) Cut a small piece of metal from an aluminum can strong enough to open the padlock mechanisms and combination locks. Keep in mind that the technique described above requires very precise cutting of sharp metal, so you need to take extra care when using this method.