Used one of the the compact lithium jump start packs for the first time on Friday evening.  Was at a venue (OK pub) to talk about filming and one of the people there had left their lights and had a drained battery when they came to leave.  (I was driving so the slightly flat lemonade was awesome (not), but the band was OK). The jump pack had been lurking in the boot for a while and when I attached it there was only one bar left on the display, but it actually started the car.  I was quite impressed as the other option would be pushing the car for a jump start, awkward as it was parked in a line on the road.  This is the one I have (loads more makers available)
https://www.halfords.com/workshop-tools/garage-equipment/battery-chargers-jump-starters/halfords-advanced-lithium-jump-starter-up-to-2l
Anyone else with useful get-out-of-a-fix ideas or gadgets?

use your drill battery

know of 18v Makita batteries being used before