We went camping and even to india with our kiddos starting at 1mos (india was at 6mos with the calmer child), and I think you are going to have a blast. I've never been big on packing toys as my kids find the random things we pick up along the way more interesting - like sticks, rocks, dirt, etc. The one exception is shovels and buckets and trucks as those things get most use on camping trips moving the dirt, rocks and sticks. Bubbles are clean fun toys and great for cleaning the kids up before meals when you aren't very close to water.
The only things I consider critical are a bumpo or baby seat, a good travel cot and a warm sleeper. The seat is important because you need someplace you trust to sit your kiddo. My favorite is actually the phil and teds that attaches to the picnic table because you'll get tired of your kiddo eating dirt after a while, and want to set him someplace out of reach of the dirt. But a bumpo would be cool too. Warm sleeper because with a 5mos old, I'm not too big on blankets and if you are in a tent, nights can be chilly. My kids both liked to have a reminder of home, and my daughter is in love with her crib, so we always pack her sleeping cot (by phil and teds). There are other portable travel beds, and even a portacrib might work depending on where you are camping. The key was to get something that you could feel comfortable setting your baby down in for a few hours while you are earshot from him. I swear I don't get kickbacks from phil and teds, I just had some specific requirements for my india trip with the little one and they happened to make a few products that met my needs of being durable, portable, small and light.
You guys are going to have a great time, and as long as you bring a safe place to sit the kid out of the dirt and a familiar sleeping situation, you are set.