EDIT: These are still working for some, but most Hiffers are receiving “duplicate” errors so I'm marking this as dead.
The free Kellogg's Family Rewards codes below look like one-use codes, but each and every one of them added 500 points to my account just now! I have no idea how long they'll be active for, so best to add them to your accounts now. Unless you're a fan of expired freebies, in which case bookmark this post until next Labor Day.
YWB1-4F47-X9ML-TZJ3 – 500 points
Z5B1-474N-6ZML-T7JJ – 500 points
K7PJ-BT1H-MT7M-T4T6 – 500 points
YJ9J-BH16-HTHM-QXXG – 500 points
FKPJ-BG1X-MTQM-1417 – 500 points
Q9JJ-BJ1R-HT4M-VXJX – 500 points
Don't forget all the current free Kellogg's codes can be found here.