City to Shore is great. I did it last year for the first time, and I'm heading back this year. The support is amazing: I somehow managed to break the bolt that held my seat to the seatpost (!), and they had me back on the road in 15 minutes. Bring what you need to fix a flat (tube and/or patch kit, pump and/or CO2). Last year, I saw lots of people with race bikes with skinny tires over on the side of the road with flat tires or broken spokes who had packed so lightly they couldn't even fix their own flat; this year, you need to get your bike inspected at a local shop before the ride if you want to be able to have their SAG team help you out (they send you a coupon for the inspection when you sign up, it's free).
They have amazing amounts of food, water, and electrolyte drinks on the way. If you have some particular brand of magic food, you will want to bring your own; otherwise, don't feel like you need to bring enough food for the whole distance.
For the 75 mile ride, the only hill to mention is at the very end, when we cross the bridge to Ocean City. We get routed on the sidewalk, not in the car lane, across the bridge. Folks wind up going basically single file, and when the person in front of you can't handle the hill anymore and stops suddenly, it's not fun. (It's really not fun when the person in front of you stops suddenly halfway up the slope to take a picture!)
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- Jeneralist