When we came down here we found it was cheaper to buy a few inexpensive chairs/umbrellas at the local Waves shop than it was to rent, plus we could take them with us to whatever beach we were visiting that day. At the end of our trip we found a family on the beach and gave them all our loot. The chairs for rent on the beach are much nicer quality though. The rates are about $30 a day for two chairs and an umbrella. You can reserve them ahead of time, but your visit is pretty early in the year, so I don't imagine you would need to. There are a few beach chair rental choices. Here's one:
Isle of Palms Beach Chair Rentals
I have no idea about bike rentals, sorry.