The phone is in my pocket and after taking a series of shots I pull it out to check them. I can zoom in and out of the full sized shots as I check for focus. It's nice to have the larger screen of the phone over the DSLR.
I can also send some DSLR shots out from my phone right away instead of waiting to get back home. I bought the Eye-Fi card after I got my Nexus 4 just to see how it worked. I was so impressed that I decided it was a good excuse to buy the Nexus 10.
It uses Direct Wi-Fi out in the field and doesn't need internet to send from the DSLR to the phone.
Having so much screen time using the Eye-Fi really eats the battery so I ordered this external battery a couple days ago.
One of the best portable phone chargers I have ever used (though its $5 over your limit): http://www.amazon.com/gp/product/B009V5X1CE/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1
Someone else suggested this same fan (but here is a link for $9.99 instead of $19.95) I used it last year in my tent and it worked great: http://www.amazon.com/gp/product/B001AVMSEY/ref=oh_details_o00_s01_i00?ie=UTF8&psc=1 (thinking about making a swamp cooler with this fan and a styrofoam cooler this year!)
If your car camping, this is can charge/run 7 different items at once: http://www.amazon.com/gp/product/B00EY6RJKA/ref=oh_details_o01_s00_i01?ie=UTF8&psc=1
Also if car camping, and will need to run your car at all to charge things, a flexible duct to route exhaust out of your campground is invaluable!: http://www.amazon.com/Dundas-Jafine-BTD48TC-ProFlex-Transition/dp/B0015UGPWQ/ref=sr_1_3?ie=UTF8&qid=1396231801&sr=8-3&keywords=dryer+vent