Every time I go outside without my dog these days, it seems to have sampling tasks attached to it. Sometimes field sampling is a few hours, sometimes it's a whole day, sometimes it's a week or two. It depends on where we're going and what we're after.
This is what I bring on a single day trip regardless of length, not including any of the equipment I need for sampling:
Bear spray. Everyone in your party should have at least one can (in case you get separated—yes, splitting off to use the bathroom counts as separating) but I recommend carrying two cans, one somewhere accessible and one tucked away. This way if you have to use the accessible can, or you fall and somehow lose it, you'll still have backup to get home safe. I carry bear spray often enough that I have a holster permanently attached to my hiking bag.
Navigation. We print out two copies of the map we are using that have all of the field sites marked (by coordinates). One copy (and a compass) comes with us in a plastic bag, just in case all our phones die, and one stays in the car for emergency services if we go missing. When we are in a place with cell service we update our contact in town with our progress and with when we finish. When we aren't in a place with cell service, we use a Garmin InReach to accomplish the same checkins, which we do at every field site. Some of these places are quite remote, and with all the hazards involved it makes our boss more comfortable the more often we check in.
First aid kit. I cater this to the field sites. If we're going somewhere where the greatest hazard is tripping on a tree root, I'll take some bandages, tape, and minimal gauze. If we're going somewhere boggy, or where we have to travel over tussocks (ugh) I bring the limb wrapping tape. In the summer I have the bug syringe thing, extra hydrocortisone cream, and benadryl for the mosquitoes. Pack for horses (likely events) not zebras (unlikely events).
Rain gear/dry midlayer/extra socks. In the summer, having rain gear can be a lifesaver. They work for wind, rain, light snow, and swarms of mosquitoes. In the winter, I ditch the rain gear and keep an extra midlayer just in case I fall through the ice. Extra socks are nice to have.
Drybag. I keep my firstaid kit in it, my portable charger, and my extra dry socks and extra winter midlayer. I also keep matches, a couple travel packets of tissues, napkins, and plastic bags in it. It goes in the bottom access part of my pack most people stick their sleeping bag in.
Knicknacks: chapstick, KN-95 mask (perfect for wildfire smoke!!), orange bandannas for added visibility in hunting season (also work as tissues or TP in a pinch), kula cloth, headlamp (for exploring holes and because it gets dark fast in winter), paracord bracelet,
3L water bladder. If we're out all day I will drink at least that much water.
Snacks. The consumption of a snack can literally change my life. I pack more than I need, because I'm the definition of hangry.
Sunglasses+hat+bug net (summer only). There's nothing worse than trying to work with bugs flying into your face. Bug net my beloved. Sun glasses and hats are helpful year round (sometimes the hat is a beanie) because the sun off the snow is brutal.
Trekking poles: some of our equipment is pretty heavy, so it's nice to have these for balance.
Backup gloves in case mine get wet
Chemical heat packs. Good for batteries, cold extremities, phones, and keeping water bladders liquid.
Cable for recharging headlamp
Extra neck gaiter just in case the one I'm wearing gets soaked completely through
Hiking crampons for icy hills
Ice axe for when ice is too weak to stand on but too thick to break through with our sampling pole.
Small ziploc of laundry lint. Makes for good dry kindling in a pinch. This goes in the drybag.
