I've been super impressed with all my Anker products and they're priced competitively. So an iPad 4 appears to have a 11560 mAh battery, so if you bought something like this:
http://a.co/41e92Yh
Anker PowerCore 26800 Portable Charger
- Colossal Capacity: 26800mAh of power charges most phones over 7 times, tablets at least 2 times and any other USB device multiple times.
- High-Speed Charging: 3 USB output ports equipped with Anker's PowerIQ and VoltageBoost technology ensure high-speed charging for three devices—simultaneously (Not compatible with Qualcomm Quick Charge).
- Recharge 2X Faster: Dual Micro USB (20W) input offers recharge speeds up to twice as fast as standard portable chargers—a full recharge takes just over 6 hours. (wall charger not included)
- What You Get: PowerCore 26800, 2X Micro USB Cable, Travel Pouch, Welcome Guide, our worry-free 18-month warranty and friendly customer service. USB-C cable and Lightning cable for iPhone / iPad sold separately.
That would handle a couple of full rechargings, it's pretty portable (3.21 x 7.09 x 0.87 in, ~1 lb) and $64 which is a solid price. You might even be able to buy direct and find a good coupon.