OP, I do a lot of the same things you are doing. A few others I do:
Field Agent--It's like a secret shopper, but so much easier. No long paper work, etc... Just agree to a job, do it within two hours, get paid. A recent job I did was take a photo of a candy bar display and answer two questions. Paid $4. There can be competition depending on your location.
Speaking of
Secret Shopping--I've done this a few times. It pays okay ($14-16) but I don't like to bother with it.
My Coke Rewards--We have mostly given up on soda but my parents buy a lot and give me the codes. Also my husband drinks a lot of Powerade and they have codes. I get Target or
WalMart cards with the rewards.
MPlus Places--This has recently gone down considerably in profitability, but I still check-in if I'm near stores. Lots of gift cards to choose.
Bing Rewards (now Microsoft)-- I get Starbucks gift cards with these.
ETA:
Kellogg's Rewards--Kellogg's owns a lot more than cereal.