if your laptop runs on anything lesss than 20v you can probably use a small lithium ion external source(rotate bouncing off the internal if necessary), the one I'm about to suggest for the mixer may work, you'll have to check the specs and do the math. For the mixer if takes a DC barrel I use a 1lb lithium ion solution. These batteries are a little pricey but are well constructed and extremely versatile.
http://powerstream.com/PST-MP3500.htmThese are also stackable which is nice. so you can double your capacity. They've been a bulletproof solution for my MOTU which is a 12v interface and now I use it on my Korg MR-1 which is 5v and am in the process of trying to wire its power cable to 4 pin Hirose to power my SD Mixpre(6-15v) on another one, the 8-way voltage toggle and usb adapter makes it a really nice solution and they last a long time for the size. The charts to do the math for how long your device will run on them is on the page I noted above. My laptop is 20v unfortunately so it draws too much juice to use one of these for it. It's probably also worth mentioning that I've had call to phone the company with questions a couple times and they have been quite responsive and helpful when I call. I have run my single battery pack at approximately 100 shows so far and have seen near negligible battery degrade.
Hope this helps.
J
P.S. - I lugged a car battery "jump starter" around for summercamp with my laptop this year and ran off of it via inverter, unless you have a wagon or some mode to transport it `without` carrying it, I would not suggest going that route.