1: Man driving wagon full of equipment and food
2: Guard room with huge beds: 3 ettins, a warrior and a 6th-level mage with a ring of protection +2
3: Guard room with huge beds: 3 ettins, a warrior and a 5th-level mage
If you talk to the guy with the wagon of equipment, he will sell you the wagon for 250 gold. He will also give you a friendly warning about how the bugbears are pissed off now that they are stuck guarding the gate and that they are afraid of the ettin as well. You could also attack him and take his wagon, seeing as he is a traitor to the city of New Phlan by supplying the evil that lives in Valjevo Castle. But that way you won't get any advice from him.
Don't go too near the wall unless you want the pissed off bugbears to come out and knock you around some. If you fight back you will blow any cover you have and then you'll be in big trouble because you won't be able to get into the gate.
Once you have snuck through the gate you will need to disable the guards. Enter the watch towers flanking the gate and take care of the guards there. Once they are defeated, go open the main gates to the forces of New Phlan by walking through them. You will need to overcome the force of bugbears that had been outside the gate, but that shouldn't be too difficult by now.