The best camera is the one you have with you and as a photographer I would say you can never have too much memory or too many batteries.
To put things in some sort of context then as I converted to digital I bought a 30gb portable hard drive as even a 256mb card was in those days extremely expensive. The hard drive cost in excess of £250.00. Today, I have not added a link as deals change all the time, but on a well known shopping site you can get a perfectly acceptable 32gb SD card for £8.99!
How many cards you might need is variable as the number of images you can get on a card is variable. In film days you knew you could get 36 frames, or 38 if you were careful, but digitally all bets are off and it varies considerably depending on the size of the sensor and the quality at which images are captured. The larger the sensor - the larger the file - and fewer images on the card. The same with quality as a raw file will use more memory than a jpeg. And then jpegs come in different quality and file size....
If you have bought a new camera recently then it will usually have a (much) larger sensor than your old one - technology is improving and being passed on - so if you are going to be using the same size card as before you will, larger sensor, get less images to the card.
I can have 12 - 15 cards with me on a trip - I shoot a lot and usually in raw. Most people will not need this much memory! I change cards regularly so that if you lose a card (fingers crossed I have not done so) or a card is corrupted then all is not lost. Incidentally there is recovery software which can be downloaded which may help with a naughty card.
At under a tenner for a 32GB card then this is cheaper than it used to be to buy and process a roll of slide film!
As for batteries, these must be in hand baggage, and I usually have 3 per body! this may sound a lot but autofocus, zooming, and chimping (looking at the image in the screen) and extreme cold all eat up battery power so better safe than sorry and if travelling then it might not always be possible to recharge every night.
Ian