I favour the "be prepared" philosophy rather than the "give up" philosophy. You don't say where you will be flying from or what route you'll take, but at least some of it will be over land. Air plane crashes vary a lot. If the pilot has some control they might be able to divert to land, or to put down on the water relatively gently. So it is worth taking what you can.

You will probably need to have it in your pockets, as you shouldn't expect to carry your hand-luggage off during an emergency evacuation. Pay close attention to the safety briefing - for example, the best crash position varies between aircraft. Remember that you release a car seatbelt by pushing, and an aircraft seatbelt by lifting (people have died from getting this wrong). Don't assume the briefing will be repeated if there's an actual emergency. There may not be time. The pilot may be too busy to keep the cabin crew informed.

Make a plan. Count the number of rows from your seat to the nearest exit in front and behind you. There should be strip lighting on the floor which changes colour at an exit, but that's not much use if the aircraft is upside down and full of smoke.

Other people have given good advice for what to carry. I'd emphasis good footware, clothing, water, and a light or two.

Personally I take a smart-phone with a lot of e-Books on it, plus one or two paper books (that don't need batteries and don't make the cabin crew nervous). Also, since you mention geocaching, it can be fun to take a GPS unit on board. Last time I went skiing I took my GpsMap60Cx, which got good signal inside the plane and on which I had loaded maps of the plane's path.