I want to make a photo-trap for wildlife
Here are my few thoughts. 


Raspberry pi needs long time to wake-up. There is no deep sleep mode support as far as I know too.  
The unwanted interfaces can be disabled, including GPU for example.. you can also keep it in standby mode. 
You can think of using a beefier battery pack. 
Think of also solar power option if feasible. 
You can use the Arduino Board or a ultra low peer board to early detect the presence (do not know your case exactly but if it am option, it can give a heads-up to Pi to boot up).