Cheaper Than Dirt sells a box lock for $10.00. You can make your own with a 3/8 hex bolt. This isn't my design. I found it somewhere on the web; maybe even here.
Drill a 3/8 hole thru the hole in the lift up handle. Get a 3/8 x 1-1/2 hex bolt, with lock washer, nut, 2 washers and 2 rubber washers. From inside the can feed the bolt thru with a washer then rubber washer. The rubber washer against the inside of the can. Then put a rubber washer, washer, lock nut, and nut on the outside of can. I find it easier to close the can by hacksawing 1/4" off the bolt. Then I drill a 1/8" hole thru the bolt and use TSA locks to secure it.
All the parts can be picked up at Lowe's or HD for around $3.00.
Hopes this helps.