Picture says it all!
I bought a set of these and an air pump for all our vehicles years ago. Originally I just had them on the trunk floor, but this sucks for two reasons:
1) They slide around when I slide the car around.
2) They’re often in the way
A third advantage is you’re lowing your center of gravity, just a teency bit 
Hard to tell from the pic, but the trunk floor sits 100% flush with these in here, and I never hear them moving/rattling. They basically fit perfect.
Need a set? These are the exact ones I purchased:
Not having a set of cables and needing a jump is a stupid reason to have to call for a tow or help.