You can with a bit of fiddling around. The easiest way to power the modem is to use a car cellphone charger that fits and is center positive. Kyocera is probably your best bet for one that fits the tiny plug.
for the lap top you can get a dc to dc in car converter. Most lap tops are 18v although i have had prof work successfully off 12v with no worries.
i could be totally wrong about the modem but this is what we did ages ago. If you use usb for the modem it get's a slight charge from that anyway.
Woosh modems are powerhogs, the supplied ac adaptor is 2.5 amps, I think it was just under 2 when we measured its actual use - those cellphone adaprers are rated noway near that much so will probarbly not work too well