When traveling in the Congo, you will (undoubtedly) come across people who wish to make your traveling a little harder than it already is. Despite all of the "fees" and "tips" you will be told you need to pay in order to pass a certain checkpoint or town, you are not required to pay any bribes or what-not (aside from obtaining a permit/visa).
The recent Bradt guide to the Congo mentions that you should carry a lot of small bills and be prepared to hand them to those who seek a bribe. This is nonsense. Though I was often asked to pay a fee or buy someone a beer, I almost always played dumb with a smile, said I had nothing on me to give (a total lie), and was able to avoid paying most bribes. In my two weeks there, I knowingly paid $10 in bribes, only to speed up my travels and avoid an argument with an armed man.
The biggest obstacle I came across was when stuck in the town of Komanda. As my interpreter and I sat down in a restaurant to eat, a man approached us. He claimed to work for the government and demanded to see my passport and permit. Speaking in French and Swahili (none of which I understand), he claimed I was illegally in the country (because I lacked a real visa), wrote my name and information down in a small notepad (his "official records"), then claimed I had to pay a $20 fee. I knew this was bogus, and so (being cheap and stubborn) I began arguing though my interpreter. Telling him I'd give him $5 or nothing did not make him too happy.
Next to us was man eavesdropping on the conversation. He turned out to be a reporter from the town of Bunia, and as he left he tried to shame the official for harrassing a tourist. Of course, the official said the reporter was wrong and that I had to pay this fee. As my interpreter was not willing to argue too much for me, he called his boss in Kinshasa. The interpeter's boss then argued with the official. But, that went nowhere as he still demanded I pay $20.
Realizing arguing with me was not going anywhere, the official decided to call his boss to see what he said...his plan being that his boss would agree with him and I'd have to pay $20. My intepreter listened-in on the conversation (in Swahili). Then, when it was over, the official stood up, gave me my passport and permit, shook my hand, said good night, and walked out. His boss had told him to leave me alone. After 30 minutes, I won the battle and paid no fee.
The next morning I came across the same man down the road at the Ituri River crossing, though this time he was all smiles, greeted me by name, shook my hand, and wish me well on my travels. The moral of this story is you don't have to pay a $20 fee in Komanda.