At age 11, most kids can handle some wait time with little more than conversation. If that doesn't work, WDW is FULL of options at every turn. I'm with those who say, the less you carry into the parks in September, the better. Except WATER and plastic ponchos, we ALWAYS carry some water! Likely, you'll also be wise to carry plastic ponchos every day.
If you really want to carry something- go as compact as possible. Your best bet is likely a giftcard! Let him pick something out of his choosing! another GREAT option is to give him a free paper park map. In Epcot, stop by the free Kidcot stations.
Classic word games are another good idea, like "I spy " and "20 questions."
Another version is to go down the alphabet naming like as many songs (or characters, or attractions, or foods, whatever you like) that start with that letter, or just name one with each letter. Can be Disney or not Disney. So I say "apples." You say, "bananas." Then I say, "cucumber," and you say, "dates," and so forth. Another variation is to name things that are red/blue/green.
Usually, our family just talks. There's no shortage of things to see in WDW (every moment), and we often find it wise to plan our next move while we are in line. Where do we go after this? When is our next fastpass? Time for a bathroom break? What do you want for lunch?
If that fails, "What did you think of XXXX?" Also give him some little jobs, like checking weather updates for pop up storms, carrying the water, keeping track of your next FP time, using the map to find your next destination.
Oh, last, did I mention pop-up showers in September? They are VERY common, and goodness, when it rains in September, it POURS. Keep that in mind when choosing electronics. On many attractions, items have to be stowed, and it is easy to leave items behind if you stow it in the WDW pouch that's under the seat.
If he is going to carry an electronic device, I'd plan a place to stow it- like a cargo short pocket + a Ziploc bag (wet rides and downpours), or maybe a fanny pack or something similar.