Just buy as many batteries as you need, plus a charger for all except the one currently in the camera. [When travelling by plane, you're not supposed to carry Li-ion batteries outside of their 'device'. I've checked with airlines that 'device' can include the charger.]
After comments This appears to not be an aviation authority rule, but one applied by airlines, who do have the final say in what they'll let you board with.
Squeezing a couple more shots out of a camera is really a futile endeavour.
Switching off live view, setting the camera to fall asleep sooner, not using the onboard flash - all these can help, but rather than constantly worrying about it, just get another couple of batteries.