My issue has never really been about cash, it's about the denominations of cash which the UK has. If we still did £1 notes in in the nu-polymer form I'd carry a fair few just for the purpose of paying for small things and fucking off the card fees for small businesses, and I'd likely just tip the balance to round up to the nearest £1.
But as things are, here in the UK - you have £5 notes as the minimum - which means paying for something that costs e.g. £5.25 means either having to carry coins around with you in advance (hassle, dirty, heavy, bulky etc), or breaking another note and ending up with £4.75 (hassle, dirty, heavy, bulky etc) in coins. I am not going to carry round coins on the off chance I want to pay for a snack or something but I'd totally carry round say £10 of £1 notes because they'd weigh nothing, can be stashed much better, and wouldn't jangle like filthy coins.