I have a 16 gb and have never come close to filling that thing up even with HD video. I always come home and download the files to the computer. I've had a few of those cards go haywire on me so I don't keep video on them long.
Keep in mind, you are only going to want to watch the same turkey strut and gobble for so long. After a while its boring. Editing is where all the work is. Good Luck!