Our family and friends love to Geocache. Go to groundspeak.com, and you can put in the zip you will be at, and find all kinds of great caches. I have found them in Ocotillo Wells, and Glamis, it makes a ride with the kids especially more fun.
Remember to bring some trinkets to put back in so the kids (and adults) can take something out, and to sign the log books. Its cool to see when someone was there last.
And leave it like you found it. Happy hunting!
Oh yeah, GPS - we use the Garmin Nuvi, because it is hand held, and I mount it in the Rhino with a RAM mount, get close, and then walk to our destination. It works well.
Any good handheld GPS will get you to the coordinates, once you get used to it.