I approached the bar, and chose to look for another way in. This gave the option to try the back door, or a small window around the back.
I decided to try the window.
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I decided to stand on a milk crate and break the window.
I climbed in, and checked the stall, only to reveal a corpse.
My next options were to leave, or open the bathroom door. I opened the bathroom door, toppling one zed over, and revealing walkers tied to a post in the center of the room.
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In merciful fashion, I opted to kill them rather than leave. The fight screen revealed 12 1XP zeds. I used melee weapons throughout the fight. After the fight, I have the option to search the bar with a light. I find a small amount of food and water supplies.
Then I only have the last option to leave.
Update May 24, 2015: Searching with a light yielded about 81 rounds of Desert Eagle ammo, I think it was.
Update March 24 2016: Searching with night vision goggles yields only food and water, but no Desert Eagle ammunition.
Another way: if you have a crowbar and flashlight/headlamp, use the crowbar to break the door, kill zeds(they can't hurt you), then search with LIGHT, you will get desert eagle ammo and a small amount of food and water. desert eagle gun can be found in office.