What's your biggest golf investment?

Definitely my 716 ap2s, but soon to be the 917 driver and 3 wood

Day to day a club membership is my biggest expense. I did treat myself to a full new bag last year. Upgraded the 910/710s to the following: 917 D3, 917Fd, 816H2, 716 TMB 4 iron, 716 AP2 5-PW, SM6 50, 54, 58 and a 1st 500 Newport SC. Had to upgrade my Jan Craig Headcovers to match my new bag too. Fun to have toys that you look forward to playing with.