Hiking in Jurassic Park, and you're only taking a handgun?
Are you nuts?
Short answer, limited to 1 handgun: Something chambered in 10mm or .45 SMC.
Long answer:
A 4-bore double rifle for traipsing across the fields.
Backed up with a 12-guage Remington 1100.
Backed up by a friend on a jeep with Ma Deuce.
For moving in the jungle...
Something chambered in .50 Beowulf.
Backed up with a submachinegun of some sort. Preferably shooting lots of bullets that go really fast. (Think a HK UMP chambered in 7.62x25mm with a 50 round magazine, and you're thinking in the right direction.)
That would be backed up with some sort of shotgun, mayhaps a PanCor Jackhammer (hey, if you can dream about hiking in JP, I can dream about having a Pancor Jackhammer, bub!
)
The PanCor would be backed up by a handgun, 10mm or .45 SMC of some sort. The pistol rounds would be loaded hot 'n' spicy.
All of which would be backed up with a really big, shiny, and sharp knife.
And I would take some friends, as well as hiring someone to tote my gun buffet.
This would only be undertaken
after learning how to go through the woods without being eaten.