I am in the field every other week for periods between 2 and 4 days, I often get out on my own but mostly I work with a small research group here in western WA.
Going out alone is not something I recommend as it can be dangerous, alone or with a team I can say that a good survival kit and handgun should be on your list.
I carry a 357 Mag, a Leatherman, a cellphone, a headlamp, a water filter, pack-able rain gear, pack-able down jacket, 5000 calories of spare food, a first aid kit, 100 Ft para-cord, a fire key, wax coated tinder, emergency blanket, spare socks and a compass.
When I am out on my own I always alert my wife and my team of the general location and around how long I intend on being in the field.