Don't own a farm or even just a bunch of property so tractors and such are out for me. I am in IT and I am the company jack of all trades (Electrician, plumber, Contractor and general "Office Bitch") so I have to say the tool I use the most happens to be my EDC Knife. Lots of guys carry them to look cool etc. I use mine at least 5 times a day on a slow day. Second most useful tool is my phone... yes most think of them as gadgets but I can do my whole job from my phone while sitting in a stand as long as I have signal. So for me...

#1 Kershaw Knife
#2 Android Phone