Something moderate in pressure (read 'classic DG round) in a double. No high-pressure UberWhompers for me, please - extraction difficulties in the brush are not my idea of fun.
Failing a double, a gone-over CZ that's been thoroughly vetted will do the job.
I'd also want a metric buttload of ammo, and sufficient time to get competent with the rifle shooting offhand, moving, and at a moving target.
Many of y'all are putting emphasis on muzzle energy. Talk to any PH, and they'll advise putting more stock in reliability under field conditions, and being competent at snap shots. Once you reach a certain level of energy (say, 416 Rigby), the returns are diminishing.
Muzzle energy won't make up for not being able to put metal on meat under duress (whether due to equipment or skill gaps).