These styrofoam pellets work really well. Wally World sells really big bags of them for around $25. The challenge is getting the pellets from inside the vendor's bag into your bag. If they can see open spaces and air you're F*cked. If they get loose they hide everywhere and actually breed once set free. You're system for getting these canny devils from the store bag into your bag has to be a closed system. I used a leaf blower/vacuum. You could use a shop vac without filter and hoses on both sides of the unit. The idea is to suck them out of the store bag and deposit them into your bag keeping the escapee numbers to a minimum.