Step 9: Hang a pulley
A pulley is great fun for kids, but it's helpful for hauling tools etc. up to the deck. Put one in now, and hang a basket from it. A climbing carabiner at the end of the rope is perfect for quick disconnects.
If you don't have a suitably overhanging trunk or branch, you'll just have to make one. Lag screw a 2 x 4 (or similar) between the two trees well above the deck (cut a long slot to accommodate movement, because you're higher up the tree), and have it protrude far enough to hang the pulley from. Bonus: you'll also have a ridgepole for your roof!