It sounds like you haven't done digital photography in a while... File sizes are much larger than your "generous" estimates--if you have a Nikon D800 your RAW i

It sounds like you haven't done digital photography in a while... File sizes are much larger than your "generous" estimates--if you have a Nikon D800 your RAW images come off the card north of 75MB (over an order of magnitude greater than your estimate). You do get a ton of resolution for that (7,360x4,912), but those files add up quickly. That would be 1,638 photos or less than 5 a day. That's shooting one frame at a time, if you're bracketing or capturing sports, you'll be shooting many frames a second and the math gets all that more complicated. Of course you can delete photos, but it's extremely easy to fill hundreds of gigabytes even keeping only your best shots.