Gear
Guide book
Portable guides are convenient to take with you on the hunt and provide immediate reference
Water
Walking, hiking, climbing ridges, stepping over trees, balancing on a rock, and squatting. It may not be the stereotypical form of exercise, but it is exercise nonetheless and is often a heck of a lot of work! Not only is it safe to stay hydrated but tastes amazing while sitting on a stump after hiking a ridge!
Compass
Many successful foragers (but not all) tend to go off the beaten path a bit and it is not uncommon to venture into unfamiliar territory. If you head into the woods going due east and therefore need to exit the woods by going due west, try alternating between spinning in a dozen circles, squatting a dozen times and then spinning in a squat position a dozen times and then tell me where due west is… Also, a compass does not die like a phone does.
Phone
GPS, satellite and terrain view, camera and the ability to save locations are all great assets to have in the woods! Oh, and safety still comes first! Downsides are potential poor service and limited battery. Several good hunting apps out there that work pretty well.
Folding Knife
If you plan on taking something out of the woods (legally), a knife will make this easier, quicker and cleaner. Strong preference towards combination knife and brush so you can cut and clean like a champ!
Basket or Collecting Container
NO PLASTIC!! Of course you will need something to carry your bounty! Baskets are preferable, but small paper bags are also popular. Separate different species. Mesh bags can work, but seem to beat up mushrooms quite a bit with all the bumping and bouncing along the way.
Mosquito/Tick spray
Nasty little buggers can turn a perfect, beautiful hunting day miserable in no time flat! Not to mention the crummy diseases a tick may have. Long pants and sleeves can also help. Mosquitos, ticks, gnats, prickers, poison ivy, poison oak, burrs all equal less fun! Up to you on brand and ingredients but deet and permethrin are kings in this arena!
Whistle
If you have an extra pocket then why not? Safety first!
First aid
Those couple of gauze pads and hand sanitizer may come in handy when you gash your knuckle open cutting through a chanterelle stem (may or may not be speaking from personal experience here!)