I am deeply understanding wickidwombat: to have a (or two or three) spares is always necessary.
And with the double slot on the 5DMk3 this camera got professional in my mind: no worries about a corrupt card or file.
BTW: 16 and 32GB seem to have the right capacity for raw. 500 up to 1000 files are not too much to remember a bit of the non- exif data in my memory, not too less to shoot something important and dont want to change the cards.
1D MKIV, lot of lenses, flashes etc
Fuji X100s, Sony RX100 III,
Fuji X- E2, XF 23 1,4, XF 18- 55 2,8-4, X- T1, XF 16/1,4, XF 55- 200, XF 56/1,2