I think you got the idea confused and/or backwards. You don't have to buy useless things in a deflationary economy. By not spending, you have more buying power

I think you got the idea confused and/or backwards. You don't have to buy useless things in a deflationary economy. By not spending, you have more buying power for when you do decide to spend (holding all other variables constant, which isn't real-world truth). Thus, inaction is more profitable than "useless" actions/goods/services. In an inflationary economy, you stick money into deposits (instead of under your mattress) because you lose less that way. These deposits are used by banks to fund loans. These deposits probably guarantee a very low but fixed interest rate (such as 0.1%), which makes a tiny dent in how much you lose due to inflation. They also make the bank lots of profit when they do well and are insured against you losing any money (except by inflation, of course) as long as your deposits total <$100k.