Edgerrin James' Money Management System ... I Keep $55k In a Box (PHOTO)

Banks are for suckers ... Edgerrin James keeps his cash -- tens of thousands of dollars -- IN A BOX.

James -- who once inked a $49 million contract with the Colts -- revealed his 2016 savings plan on social media ... a plan that would make the people at Fidelity lose their minds.

Here's James' explanation ...

"This is my 2016 Vice Boxxx savings... I put away $100 a day & $200 on weekends -Fri/Sat... (Any $1, $5, or $10 in pocket at the end of the day goes in there also)"

Don't laugh, the guy saved more than $40,000 ... and he's got so much, he's actually holding a contest to give $500 away to whoever can guess the exact amount.

Good luck ...