Obviously, with that, there are some other reasons:
It's Safer Than Leaving It Up to Him
How many times have you been in this scenario: Things are getting hot and heavy, clothes are off, foreplay is happening. You're both ready to just do it. You tell him to get a condom, and his face goes from looking like he just won the lottery to looking like he just saw his grandparents take part in an orgy. He doesn't have one. What then? Either the sex just stops and no one is happy, or (being so caught up in the heat of the moment) you go through with it anyways. You might think that he'll pull out, or that you'll take the morning-after pill just this once. Plenty of women have been in this type of situation, myself included. Obviously, there are risks involved with condom-less sex—way more than accidental pregnancy. Whether you've gone through with the sex or not in this scenario, in either case, wouldn't it all have been so much simpler if you had your own condom?
Yours Might Be Better
Guys tend to have a preferred brand, or type, of condom. You can too. It's not a bad idea to experiment with condoms. For instance, while most are latex, you might find that you like non-latex better. There are also condoms that vary in thickness. You might find more pleasure from a thinner condom. Then, of course, there are the ribbed ones. I've never felt the supposed extra pleasure they claim to have, but you might. Same goes for condoms lubricated with special ingredients to provide warming sensations. Try them all out, and pick the ones you find the most pleasure out of. It could very well be that all of them feel the same to you, but you never know until you try. One or two of them just might go above and beyond, and if that happens, you're going to want to have those condoms on you at all times. *