How can I increase my Samsung Galaxy Tablet 10.1 battery life?
According to your usage scenario your best bet would maybe be to get one or more of those external Li-Ion battery packs:

The higher their mAh value, the longer it will last. Currently there are offerings for 12.000 mAh packs, that's about double the size of your current internal battery size. Maybe buy one smaller unit first and see how it performs.

Here's a search link for amazon:
http://www.amazon.com/s/field-keywords=usb%20battery%20pack