Usually your Mac Book does a special thing, that is called "safe suspend", what happens here is that the RAM content gets written on the harddrive, but the Mac Book is not turned off, only put in sleep mode. This is just a safety feature, if the battery would run dry, it still can restore the content from the harddisk, otherwise it will just come back instantly from the sleep mode.

If you travel a lot, it is imho better if your notebook does a "normal" supsend to disk, since this will turn off your laptop completely after the contents of your memory have been written to the harddrive and preserve the battery way better compared to sleep mode. Changing this is easy, but Apple didn´t put a GUI for that into Mac OS X.

So there are two ways to change this: either the console or a UI called SmartSleep (which is freeware): 

(just use the one of this commands that fit your needs best and reboot your Mac Book afterwards) 

• sudo pmset -a hibernatemode 0 
  (always regular sleep (disable safe-sleep))
• sudo pmset -a hibernatemode 1
  (always safe-sleep (disable regular sleep))
• sudo pmset -a hibernatemode 3
  (regular sleep first, safe-sleep if the battery is very low on power or is unplugged)
• sudo pmset -a hibernatemode 5
  (always safe-sleep with secure virtual memory)
• sudo pmset -a hibernatemode 7
  (regular sleep first then safe-sleep with secure virtual memory)