It's actually super smart to have that tote of stuff started! I buy Disney tees and little trinkets to give them on the trip to make it feel like they are receiving souvineers each day. Last trip they ended up buying one thing each on the last day because each day they'd wake up to glow sticks and a new tshirt so they didn't even ask for more. I frequent the Disney shop at JcPenneys. I have found t-shirts there as recently as a few weeks ago for $3.99. H&M can have some cute Disney things every now and then for super cheap as well. Last year I found my boys storm trooper mini backpacks for $3.
Make sure to go to
Walmart or Target to get a light up spinner to take for nighttime shows if you think the kiddos might want some of the fancy expensive wands that come out just in time for fireworks or nighttime shows. We found some with different characters for $3 each at Walmart and I was sure to put them in the park bag before we headed over when I knew we'd be staying for nighttime shows.
As far as fastpasses go, since you'll be starring clear of rollercoaster I will give you a list of smaller rides that tend to have longer lines (you will want to fastpasses these or ride them after ropedrop).
In the Magic Kingdom you will want fast passes for 3 of the following attractions; Peter Pans flight (almost always a long wait without FP), Enchanted Tales with Belle (not a ride per se, but an experience you won't want to miss), 7 Dwarves Minetrain (kind of like a mini-coaster), Buzz Lightyears Space Ranger Spin in Tomorowland and Pirates of the Caribbean or Haunted Mansion. If you want to see the only taking Mickey in all of Disney,then you could fastpass meeting Mickey at the Town Theater. Most other things can be ridden in the am or evening with minimal wait times hopefully.
In Epcot your best bet is attempting to FP Frozen Ever After (hard to snag sometimes), then the Seas with Nemo and Friends and maybe Turtle talk with crush or the character spot with Minnie , Mickey and Goofy? We loved eating at Akershus Royal Banquet for a late breakfast at around 11. This allowed us to meet many princesses and not have to stand in line and it was cheaper than eating at the castle. Since my kids are picky eaters breakfast worked out better because I was sure they wouldn't try the food offered for the other meals.
At Hollywood Studios get fast passes for Toy Story Midway Mania, Frozen the sing along and maybe Star Tours (even if they aren't Star Wars fans it's fun!), or maybe fantasmic if you are up for staying late and seeing a nighttime show, this is a good one. If your kids are Star Wars fans there's a free Jedi training program but you'd have to be at the park an hour before rope drop and go straight to sign up to get on the list of participants and it can be a mad dash of crazies! I hear that both as Sci-Fi dine inn and 50s prime time cafe have very cool theming for a sit down meal at HS.
At Animal Kingdom definetly fastpass Kilamanjaro safaris, Na'vi River Journey and maybe Kali River Rapids if you like an adventure and don't mind getting a little wet. One of the best tips I took for animal kingdom is that Yak and Yeti quick service window has fried rice as a snack credit that really could be a good lunch for most. It's super inexpensive and was pretty good! We only did AK half a day last time because Pandora wasn't open yet and we were exhausted by day 4.
That would be my next suggestion, either a break day or half day for R&R. The crowds and all the adventuring can take a toll on any of us and to make the time more enjoyable don't hesitate to go for midday breaks/naps or just have a resort day. FQ has a great pool and new splash area just for little ones and there is evennthe chance to ride carriages around the grounds(reservations highly recommended). Or sleep in and take a boat ride from the resort dock down to Disney Springs and check out the World of
Disney store or take a free pic with special backdrops at the photo pass stop( you can buy the ones they take, but they will take pics with your camera as well, for free!).
Gosh I could go on and on.....I hope my suggestions are helpful. No matter what you choose, I know your trip will be magical!
One of the main reasons I want to make the reservations (besides characters) is it is just going to be me and this way I don't have to try and find them something to eat and then trying to find a place to sit and eat it. And we can sit in air conditioning for a bit. Oh what do you do with your strollers if you have one while at the character meals? Which attractions would you suggest for fast passes? I am planning on us getting there at opening and trying to do all the little rides first. 
