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I would suggest you wait and see as you don't know when they got eaten. Its probably late to induce vomiting.
I'd suggest adding some high fiber food to his dinner or as a snack now to help him pass the items through. Fiber bulks up stool and keeps it moist and easy to move through the system and may help him pass the straps.
A slice of high fiber bread, a couple of big spoonfuls of plain canned pumpkin or even applesause may help him pass these.Some people use metamucil which you can read about here
scroll down the page for all the info.
Dogs that use that need to take in extra fluids so you may want to make some dog 'soup' by mixing water with canned food or baby food meats to encourage him to drink extra.
If your dog has abdominal pain, vomiting, diarrhea, or constipation, stops eating or appears ill then see your vet as you may need to get the rubber removed by them.
Hope this helps you!