List of items available in every game (some spoilers)

[dainbramage]

Old shoes, clay bowl, cart wheel, dwarven beer (training)
The 3 paintings from the artist (for last 2 you need to finish the quest)
Miner's helmet (always at Mehgard)
Steam armor and Drill (Mehgard, after finishing ellinia)
Adherent's staff (after finishing magic range)
Kerus's Sword (can buy after ultrax quest, might also have to talk to xeona about it?)
Pirate flag (accept from the guy with the fat wife who owes money to brotherhood)
Barbarian shield (take the head from freedom isles to the barbarian camp in verlon)
Roast rats (7 from talking to miners in lucky james mines, 1 from fish stomach)
Gremlin castle (taron anytime)
Ale barrel (beer quest)
Old Skull (karrakh, second encounter)
Purse (escorting the annoying dwarf)

And you can also get the ale barrel, staff and dragon-slayer's sword randomly as well as the guaranteed spawns