Most Apple laptops have an SD slot. It’s not super fast, but it provides a handy slot for inserting up to a 512GB card, which even in its tiny case fits into a wallet—really small.
B&H Photo has the Lexar 64GB SDXC card with card reader now for only $84.99. This rockin' fast card is now my favorite and the card in that card reader hits about 300MB/sec! Great for big downloads at the end of a long day and far faster than using a built-in SD slot on a MacBook Pro.
In the past I trended to using CompactFlash cards, but that standard has lagged in both speed and capacity and it is sometimes a hassle to have to use an external reader. See also:
Even though it’s not the fastest card, I also like the Lexar 1000X 256GB SDXC for a simple reason: I can make a backup of all critical data and stick it into my wallet and not even notice it being there. Very cool. Get a 2-pack of Lexar 1000X 256GB cards for $275 (as this was written).
I hugely prefer high-capacity cards (64GB or larger) because in the field there is no need to erase them, thus they are an additional backup over and above downloading the day’s shoot (and backing that up too). Aside from cost, I’d be buying 128GB or larger cards for that reason, but for now 64GB serves me amply for most of my trips (not filling up).