The most secure and long-lasting closures for plastic ice bags is to use hog ring staples.
11/16" Ice Bag Hog ring staplesare made of 16 gauge heavy-duty galvanized steel wire that can be bent while maintaining strong holding power. Hog ring staples can be used in pneumatic hog ring guns but for securely sealing ice bags it is best to leave them in a "stick" formation and insert them into the Bostitch P7 plier. They can be loose-packed in a plastic bag but Ice Bags Direct doesn't recommend it. Download the attached "How to Operate the Bostitch Hog Ring Plier for Bagging Ice" for detailed instruction on how best to operate.