Know how to use your map and compass. Good sturdy boots with non-slip soles and ankle support. Some people prefer gumboots if working in marshes. Make sure they fit. Do not wear sneakers.
Heavy wool socks to prevent blistering.
Strong loose cotton pants help you move in brush and will not tear. Wear a belt. Long T-shirt to tuck into pants. Helps prevent chafing with backpack and makes it harder for blackflies to bite you. Long sleeve shirts that button up to the neck to keep flies out.