Avocado toast (n): a cheap luxury, especially one which is perceived as being very expensive but is actually trivial; can also refer to the trivial cost thereof.
"Oh, hey, when can I drop off that fleece you loaned me?"
"Nah, keep it. It's just avocado toast."
Avocado toast (v): To reduce your spending by a trivial amount, (i.e., by the cost of avocado toast).
"Oh shit. How are we going to pay to fix the car?"
"We could... stop eating out?"
"The frame is bent, it's leaking coolant, and the front bumper is in a tree. I don't think we can avocado toast our way out of this."