What's in your fieldbag?

Hello! I'm about to embark upon my M.sc in Marine science. This is very new for me as I majored in a different field during my B.sc. Very different haha. So now I'm in need and I'm curious to know what my fellow scientists and science students keep in their fieldbag for when you're out doing fieldwork, excursions, surveying etc?

Any tips, tricks, or ideas are more than welcome.

Thanks in advance!