Parts of the Rivendell scenes were shot as pickups, after filming was done. Sam in those shots is a much thinner hobbit, because after the final wrap, Sean Astin lost the weight he had gained to play Samwise Gamgee.
When Merry and Pippin have just taken the dragon firework from Gandalf's cart and are in the tent tossing it back and forth, Pippin shrieks when it goes off. Apparently, Peter Jackson had told Billy Boyd it would only spark and fizzle, so he was fairly surprised when it shot off in his hands. He talks about this in the commentary on the DVD.
When filming "Fellowship," the actors playing the Hobbits required hours of work just to get on their Hobbit feet. It was so long and terrible that Sean Astin (Sam) counted the amount of times they had to put their feet on when it never showed up on camera in that day of filming. The final count was 50.
When the four Hobbits are in the woods running from the Ringwraiths, they run onto the boat at Buckleberry ferry and go to Bree. Merry, Pippin and Sam get on alright but Frodo has to jump. The first time the filmmakers shot this scene, Elijah Wood jumped right over the ferry and into the water on the other side.
When running away from the Balrog, Boromir is the first to reach the bottomless stairs and Legolas pulls him back to safety. When this piece was shot, there were many retakes, and each time Sean Bean would get pulled back by Orlando Bloom, Bean would land back onto Bloom's soft lap, while Bloom would slam back onto the hard steps with the full weight of the two of them. As a result, Bloom had bruising on his backside and legs, for some time. Bloom joked, "I gave Sean a few beatings for that, I can tell ya." Cast commentary, extended DVD.
According to the book, Frodo is the oldest of the Hobbits in the Fellowship, but Elijah Wood, who plays Frodo, is actually the youngest of all the Fellowship actors - he was seventeen when filming began. The actors who played the younger Hobbits (Merry, Samwise and Pippin) - Dominic Monaghan, Sean Astin and Billy Boyd - ranged in age from 23 to 31 at the beginning of filming. Ironically, in the book Pippin is the youngest of the four Hobbits, whereas Billy Boyd, who played Pippin was actually the oldest of the four actors portraying the Hobbits.
Sean Bean (Boromir) was deathly afraid of riding in the helicopter that had to take the actors to and from the many filming locations. After the scene on Caradharas, the one where Boromir tries to take the ring from Frodo, Bean refused to go anywhere else by helicopter. Many times he had to take a ski lift and climb many hundred feet in full Boromir gear to get to the set.