With regards to Profession, it's pretty wide open, you can make up almost any profession that makes sense for the campaign world. Ones I've seen in the SRD include bookkeeper, miner, sailor, herbalist, siege engineer, and hunter. You can pretty much make it up. Jeweler, gladiator, mercenary, tour guide, pastry chef, or whatever else you like :)
While the primary purpose of Profession skills is RP flavor and the ability to turn a profit during campaign downtime, If you get 5 ranks in a profession, I'll grant you a synergy bonus of +2 to a skill or two that make sense, in conditions that make sense. For example, Sailor would give +2 on Swim checks, and +2 on Rope Use aboard a ship (rigging, moorings, etc). Profession (Merchant) might give +2 on Appraise checks, and +2 on Diplomacy checks with other merchants.
Sometimes a Profession skill might give you an option to substitute for a skill check that would be more difficult otherwise, for example, you might be able to just substitute Profession (Sailor) in place of Rope Use if you're handling a ship's rigging in a storm, and since it applies specifically to the circumstance your DC would be like 5 lower or something. There's no hard and fast rule here. Use your imagination, don't get attached to specific mechanics on this one.