Backpack Dry Bag liners work reasonably well. You just put one into your backpack and put your gear into the dry bag then use the roll closure to make reasonably waterproof.

http://www.outdoorkit.co.uk/product.php?product_id=2464

http://www.nomadtravel.co.uk/catalog/view/ortlieb-rucksack-liner-and-dry-bag-

Waterproof back pack covers works quite well at keeping most of the rain of the back pack as well.

http://www.outdoorkit.co.uk/product.php?product_id=2454

Reversible Camo/Hi vis waterproof back pack covers are quite useful.

http://www.wildlifewatchingsupplies.co.uk/trade/acatalog/Rucksack_Covers.html

Otterbox will probably have a waterproof case for most small electronic gadgets

http://www.otterbox.com

Last year, while on vacation, I found these awesome bright orange swimmer's cases designed to keep personal belongings dry, but are perfectly sized to hold an altoids tin plus a few other items around the edges. Still playing around with that (and wishing I had bought more than just one of them ).

As for in the pack, I am taking notes and plan to try out most of the options mentioned when the time comes. I figure ziploc freezer bags will be the way to go as I hope that between the pack rain cover and my own poncho that things will remain relatively dry. I hope I come out with at least a dry pair of socks anyway. Hmmm ... I sense some testing in the garden tub in our bathroom coming on. Great topic frisket.