I always have as little as possible (just enough for island) when actively playing. When I go to bed though I try and stay below 100k (50k or more) for space and so its there and ready for when I get on so I can scour the shops and HHS.
i carry 89,000 bells at all times. no more than 99,999, and no less than 82,000. any extra bells are placed in one of the spare letters in my pockets until i feel like depositing it in the bank
Usually more than 10k, but anything up to 90. I like to pay off loans etc in 100,000 chunks until the last little amount, so whatever's left in my pockets once I've used up full 100,000s is what I carry xD!!
I try to keep 30-50k on me, but I only deposit when I have to use bell bags, so it can be anything. I keep my bank account with five 0's at all times. ~ Even if I have to have stuff converted to bells on the island, I will then empty box and sort money and usually end up withdrawing 50 bells alone. xP I've done this on every AC game so far.
Though currently my bells sit at 977. xD I just emptied my account for a PWP and house renovation and perfectly used up everything I earn off turnips. Guess it's cheap living for the next few~