Can I also use Wi-Fi usb sticks on my laptop if I have no fixed wlan / lan connection eg in the woods or when camping?
Without wireless router in range no internet
Then you need an Internet / Surfstick
If you have a public Wi-Fi network while camping or in the forest, then if you do not, then a normal Wi-Fi stick will help you a little.
Unless you have a stick in which you have a SIM card and you use the mobile. Then that goes everywhere where you have network connection.