One of my favorite activites is in the Marilyn Burns book, About Teaching Mathematics (which by the way if you don’t already own you should DEFINITELY get, not just for perimeter lessons but for every area of math – I find it indispensable). In this lesson the kids trace their own foot onto a piece of centimeter-square graph paper. They look at their foot tracing and estimate the perimeter. Then they lightly tape a piece of string along the tracing line, then unstick the string and measure it. The use of the kids’ own feet adds a great hook for their interest and attention to the meaning of perimeter.
Incidentally, once you start studying area, the foot tracings again come in really useful. The kids can shade in each square unit and keep count as they go (it’s great to have them debate the best ways to keep track of how many they have shaded – in groups of 1, 5s, 10s, 100s, etc). Then they can also shade in the partial square units, looking for pieces that together make a whole square unit. This activity is fun, meaningful, and has the added benefit of being good practice for those questions on the standardized tests that ask them to estimate the area of a circle, or some other shape where they need to visualize partial units adding together to form whole units.