On the last part of the mission where you must put Captain MacMillan down by the Ferris wheel and wait for the helicopter, you can get an extra full round of claymores. Before putting MacMillan in the grass where he tells you to, put him down anywhere else so he doesn't call in the helicopter yet. Take the opportunity to go around planting the claymores you already have, then pick up MacMillan again and place him in the area he wants to be placed at. He will tell you to plant some claymores and give you a fresh batch. You now have a full inventory of claymores again to plant. Note: Avoid planting them where the enemies come from (behind the buildings) since as soon as one explodes, they all start crawling around and are harder to kill. Try to plant them near cars where enemies hide behind to destroy the car and kill two or more enemies if you are lucky.