Many geologists chose the field because they enjoy being outdoors in quiet places (like the roadcut along I-70 west of Denver?), but day after day - or week after week - spent climbing limestone cliffs and bushwhacking through forests means that your favorite geologist is going to need some gear. That's beyond the essential tools of the trade, but I'll get there, too.
What to Wear: Let's Start at the Ground
Field geologists don't spend their days sitting around: they spend most days on their feet, often nowhere near a trail. Solid hiking boots are an absolute essential: sneakers just won't cut it. Choose boots that go over the ankle for the extra support and have tough, deep-lug soles for the added traction. This is one item to splurge on if possible, because your hiking boots will be a long-term commitment and they absolutely must be comfortable.