I helped out a tour company with the beginning 3 days of San Fermin in 2012. Although it was a cool experience, it was also totally insane and like nothing I've ever experienced. Imagine a drunk night on stinky/dirty Bourbon St. or a drunk, muddy time at something like Chilifest...and then multiply that by a lot.
The need for a tour company depends on what kind of travelers you are. It can easily be done without and would likely save you lots of money. I wouldn't have spent money on the tour company that I was helping out, except the cool thing was they had an apartment on Calle Estafeta, which is on the route of the encierro each morning. The apartment had two balconies so I had a sweet view of it all. The crappy thing was it was so.damn.loud the entire time because the party is all hours of the day and night...let's just say I didn't any sleep until I was on the train leaving Pamplona heading to Madrid!
Only those of us working with the company slept (or tried to) at the apartment. The guests stayed at a hotel a good distance away from the craziness, so it was quiet where they were. They did, however, get to come to the apartment to watch the bulls run, watch it on tv, eat breakfast, etc. as it was set up as a hospitality room.
Some other things we (as guides) did with the guests: greeted them upon arrival and helped get them to their hotel, took them on a walking tour of the area the day before opening ceremonies (before the streets were full), had a happy hour/dinner their first night there, hospitality room at the apartment, went to the bull fight together, was a point of contact with anything else they needed/wanted help with. A t-shirt, red scarf, canteen, bullfight tickets and not sure what else were included in the package. There were I think 3 waves of guests that came for about 3-4 days at a time, so some were there for the beginning, some during the middle, and some for the end.
That being said, and of course depending on what kind of travelers you are, you could easily do this trip without a tour company. You should book a hostel, hotel, something. Although there are many people that sleep on the ground, on park benches, etc., at some point, a bed, bathroom and shower might be nice. Although many people use the streets as a bathroom - no joke. It's gross and smelly (worse that stinky Bourbon St.!). The bus system in Pamplona is really easy to use. You can easily take a bus from the train station to get to your hostel/hotel, or a nearby stop and walk some. There are also taxis you could always use. There are TONS of places to buy red/white clothing if you don't come prepared or want something that specifically says Pamplona or San Fermin on it. You can buy bullfight tickets once you're there. You just might not have a cool balcony view of the encierro. Obviously, if you're running, you're street level, but even if you're not running (or you want to watch the first morning and wait to run the next) you can buy an inexpensive ticket to be inside the arean for when the bulls run and arrive in the morning.
Make sure you have your train tickets purchased in advance because they'll be sold out with people leaving Pamplona...in other words, don't expect to be able to arrive to the train station when you're ready to leave Pamplona and just buy a ticket and go. Buy it at the station or online ahead of time.
As for packing...anything you take to be worn during San Fermin, plan on it getting dirty, stained from sangria, and leaving behind! Take white pants/shorts, white shirts, red bandanas/scarves, a hat (for sun and/or keep sangria from getting in your eyes, hair or all over your face!), sneakers that you're prepared to ditch - they will be GROSS after walking the streets of Pamplona! The most brilliant hat I saw when there was one of those miniature umbrella hats. Money belt to wear under your clothing - you won't want to carry any sort of bag/purse with you if you plan to walk the super crowded streets. Maybe a draw-string bag, something that's small and you can keep close on your body. Zip-locs for your phone/camera (even if in your pocket) - there's a great chance you'll take a sangria shower at some point.
Be sure to look up the rules for running...some are pretty specific and you have to be in certain places in the morning in order to get in. You're not supposed to have any kind of camera, phone, go pro, can't be (too) drunk, etc. So just check the website and I think they have rules posted near the route. If you have any questions, feel free to email me! (goldentista03 AT gmail DOT com). Good luck!
