Flash Cards are offerering more and more storage capacity, this is necessary because the more megapixels a camera has, the larger the file is being saved. What you should not do (especially if you are on holiday for example) is to save a lot of files on one flash card. If you lose the Card or it gets broken you lose all your files. It's better to use multiple cards and save your files regularly on an Image Tank or a laptop.
Try to resist the temptation to delete photo's while you are shoting pictures. Only on a big screen, you can make a good judgement about the quality of a photo. I have several times used a photo which I initially thought it would only be suitable fot the "trashcan" ...