No, you don't need the Hallmark brand, but let me tell you, working in an office setting you will ALWAYS want to keep a stash of cards in file. Whether your boss needs one, or a coworker surprises everyone with the news of an impending retirement (or a baby), a stash of cards will come in handy. And of course, this also is a trick that you can use at home.
You will want to go to the Dollar General and pick up some cards, since they often have 2 for $1 cards that are so much better than the generic "in the box" packages. Just pick up a few happy baby cards, some birthday cards, some blank cards, and a bunch of SORRY for your LOSS cards. Yes, before I started work I had no idea how many people lost family and friends so often. Clearly I was in my own little world, because these are the most needed cards in my stash.
Another thing to keep in your personal stash of cards is one or two small gift bags and tissue paper. You will need this at least once a year. While you can usually run out to get a one dollar lottery ticket for a card, or a $5 coffee gift card, there will be times that will require something a little weightier, and you won't want to have to stop at another store to buy a bag and paper.
These are just a few of the necessities for looking like the most "together" staff member in your office. I'll have some more suggestions coming up. In the meantime, feel free to add your tips in the comments. I promise I'll read them. I might not publish them, but I'll read them! :)