Footstrap bolt shears the thread: if you have multiple footstrap holes, simply use another hole. If not, try to source a larger width bolt. If you are already using the largest bolt, grab as many tiny sticks you can on the beach and break them off in to tiny sections and jam them in to the hole as tightly compacted as possible, then try the bolt again. It won’t be as strong as original thread but this will work for a temporary fix!