I feel the litter issue. I think the most we ever did was buy 4 of the huge tubs when Target had some ridiculous offer, like “$5 off a purchase of any 4 from these brands” type of thing. But the need for litter never ends, so I’ll take any of those deals any time I can get them.
We did use petsmart.com last time we got cat food because they had a free shipping deal on purchases over a certain amount, which was not hard to hit once you bought 2 bags of food. Adding litter to the order might work there too? Haven’t tried that yet.