I use my iPhone 4S more than my point and shoot waterproof camera....unless it's raining.
I have it in a carbon fiber
Element Ion4 case that has saved it from many drops, including one from 12'. I'm not suggesting this case necessarily, but some sort of bumper protection will go a long way, just make sure it's not too rigid because it'll transfer the energy to the phone inside it. I have seen cases as low as $5 that would probably work just as well.
I also have a
Zagg screen protector on it, which is lifetime guaranteed. It protects the screen from all sorts of scratches, whether it's dirt on your fingers or having the screen touch rocks if it scraped across them, like when it's dropped
. I have found the Zagg products to be excellent and their customer service top notch. I work with a lot of nasty chemicals and do side work automotive (think grease and oil) and it also protects from both of those.
I had the Otterbox Defender and while it provides some protection, it's bigger and clunky compared to just the case and screen protector, and isn't waterproof anyway, just water resistant. I looked into the Lifeproof case since it is waterproof, but the screen layer the Lifeproof and Otterbox add makes them harder to use since additional tactile pressure is needed. The Zagg screen protector is just like using the bare screen by itself.
For hiking, I either keep it in a side pouch ready for use as described above, or inside a freezer bag (they are tougher than regular ziploc bags) on the pack belt. If it's a long hike or raining and I'm using my point-and-shoot camera instead, I have two lexan waterproof/crushproof hard cases I use, which I can provide the numbers and dimensions of, but I'm not sure of how the S2 compares to the 4S dimensionally.
For biking I just keep it in the top pouch of the Camelbak but will put it in a freezer bag if it's going to rain. For Kayaking I always put it in one of the hard cases since they are waterproof and will float should I dump the kayak. I also tether the case to the cockpit and am just careful with the phone when I remove it.
One thing I also take with me, that I love using, is a mini tripod for self pictures. It's a
Gorilla Grip Tight Stand and I bought it at Beans. It holds the phone really tight and sets up in seconds. It's so small I also keep it in the waist belt of the pack right with the phone. I had the tripod already and just bought the Grip Tight by itself, but there are a few
options. It's money well spent.