Do I need a coffee grinder?
YES. Otherwise, you might as well be drinking grocery store coffee.
During the roasting process, coffee develops many beautiful aromatic compounds that give coffee its flavor and aroma. These aromatic compounds are largely trapped by the physical structure of the bean, dissipating by about a month after the roast. However, the grinding process breaks up that physical structure, releasing the aromatic compounds immediately.
After grinding, you've got about 15 minutes to brew your coffee if you want to preserve all the most delicate aromatic compounds! Once the coffee is dissolved in water (i.e. after you brew it), the aromatic compounds stick around as long as the coffee tastes good.
That said, grinders aren't too big an investment. You can get a cheap one at a big-box store for $10-20, and it's totally worth it to do so as long as you're drinking specialty coffee. You can also use a blender or a food processor in a pinch. If you look in antique stores, you might be able to find a nice old hand crank grinder, which are always fun, plus they make great coffee in a French press and they're perfect for camping since you don't have to plug it in. For a super low-tech solution, you can always put the amount of beans you want in a heavy plastic bag and use a rolling pin or even a wine bottle to crush up the beans.