are - are you seriously just now figuring this out? I've always been carrying mine with me, I get my 10 coins nearly every single day. And if I meet with my friends, I can get 3 street passes a day as well.
I had a giant reserve of coins when the new streetpass features came out, it was great.
Pah, what the cool kids do is the jack off motion with their 3DS 1000 times a day to get the 10 coins.