PP has a lot of my same ideas.
Free ice water. I rarely (if every) buy a soda in the park
Flavor tubes for water bottles (I made straps to carry the bottles so they are very easy to carry-everyone carries their own)
Share meals-many of the CS meals area shareable between 2 A or 1A and 1K.
Eat breakfast in the room. Fruit, poptarts, cereal, toast, etc. Saves time and money
New ones
Also you can order a
kid's meal for an adult at the CS locations if you aren't too hungry and it inc. a drink.
You can carry some food/drinks in with you. Nothing in glass. I've carried in my own cans of Diet Coke (get ice for free) as well as some snack type items. No reason why you can't carry in certain types of sandwiches as well (they kind that don't require refrigeration.
My DD10 and I go to DLR a lot and one thing we do to save a little money is when we do get ice cream we share a 2 scoop one. We each get one scoop of our fav. flavor and it's cheaper than ordering 2 singles. I usually ask for an empty cup to put one of the scoops in. If we are getting a sundae I ask for the sauce on the side since my DD doesn't like them. We share the cone.
A single cone at MS Ice Cream is $2.69, a double is $3.69. Only $1 for the extra scoop. So instead of costing $5.38 for 2 cones, we save almost $2. Not a huge savings but it adds up.

At Fountainview in EPCOT the prices are:
Single Scoop $2.69
with Waffle Cone $3.09
Double Scoop $3.69
with Waffle Cone $4.09
Same for regular cone, even more savings on a waffle cone ($6.18 for 2 singles vs. $4.09 for one double-over $2 savings.)
We always have a rental car so before we even get to our resort we stop off at Super WM or Super Target to get breakfast items, water bottles, sodas, and if we don't have one in my fridge swap, a cheap toaster. You can use the toaster and microwave in the food court but sometimes it's just easier to use your own toaster in the room.
You can take ice chests into the water parks. Again, nothing with glass or alcohol.
Can't help you with locker locations. Sorry.
HTH.