What would be a reasonable amount of money for this vacation?

Alright! So, i'm turning 21 on June 23rd, so my mother, my niece and another friend and I are planning on going on vacation to Myrtle Beach, SC. We plan on staying from June 21st to June 25th. I already have the hotel prices worked out, as well as car rental/gas (My own car is not in good enough shape to take that far so we're having to rent) but I'm having issues with the OTHER expenses, and figuring out how much money I should have on hand. Here are the factors I need to add up for:

~Going out to eat once or twice a day (Also plan on going out to drink at a bar or something on the 23rd since i'll finally be 21)

~Not sure what attractions are there, I haven't been there in over 7 years, so money for attractions.

~Money to buy some souvenirs or other random things. I enjoy looking at pawn shops there because they always have lots of them, and lots of good items.

~Money to buy things like sunscreen, water toys, towels, etc.

Note that I DON'T want my friends/family's expenses added in. They'll be paying for themselves in terms of attractions, souvenirs and other things, but we will most likely be splitting some of the restaurant bills.

So, based on this, what would be a good amount of money to have on hand AT LEAST?