In my opinion, a ~5,000 mAh external charger is the perfect balance between size and capacity, as long as you can charge it every night. RAVPower makes some of the best chargers around, and their 5600mAh variety is only $15 today. [RAVPower 5600mAh External Battery Charger, $15 after promo code C4VIOZCK]
Today on eBay, take $110 off a 32GB iPad Air, or $120 off the 64GB model. Most iPad deals these days are only on the 16GB flavors, so this is pretty notable.
More of an Android fan? There's also a Nexus 7 available for $130.
Apple iPad Air 32GB ($490) | eBay