If you have City Navigator maps in your 705, you have the same POIs as the car GPS.
Menu>Where To?>Find Places> then you can choose "Gas Station," "Food and Drink," or if you want to find by name, go to Others>All Categories> then spell the name.
Now, that said, what's "nearby" might be a good bit out of the way by bicycle, and my experience in the car with DH's Garmin GPS is that the database of gas stations is not very up-to-date, even with the latest maps. So I would plan ahead, search on the web for businesses in towns that your route passes through, and if you'll be riding on a Sunday, make sure they'll be open.