That's 120Whr per day, times seven days, 840Whr for a week.
So a 60 kWh Tesla Model S would power a Pi for over a year and it meets the "portable" spec by virtue of being self-propelled.
Seriously though, there exist marine deep discharge batteries available in the 100+ Ah range, but that's a lot of battery and they aren't cheap.
Without knowing the specifics of the application, I wonder if a commercial Android phone or tablet might not be a better starting point as they have better power management, particularly if you don't need continuous operation. That is, if you want the sensor to wake up periodically, take a picture and then go back to a low power standby mode, you can get by with a lot less power. The downside it that the learning curve to programming such a device is much higher.