This really isn't a good contract. There's no reason for non-signatories to contribute to the trinket account, they get nothing from it as the 2 units of product go only to the signatories.
So? I don't expect them to do it, but there's no reason to ban it.
For that matter, since there's no provision for mandatory trinket funding, there is also no reason for signatories to contribute either, since they're getting 2 units from a successful voyage regardless of whether they contributed 2 Florins or absolutely nothing to the trinket fund. It's in the best interest of everyone to not contribute and free-ride off everyone else in a game of financial chicken until someone goes bankrupt.
An absurdity, since, if nobody contributes to the fund, no voyages happen. It's not a Nash equilibrium.
It's not an equilibrium, but it's still unfair. Let's say you and I are signatories, and after buying the ship, we both have 1 Florin left. You also contribute 4 Groschen and 4 Pfennigs to the trinket fund, while I do not. You now have 5 Groschen and 6 Pfennig left, while I have 1 Florin. I stubbornly refuse to contribute anything to the trinket fund for a few turns.
Now you have two options: either contribute further to the trinket fund to cover my part and get the ship moving, or not. If you do the former, the ship sails and returns, and both you and I have gotten 2 units of product as per the contract, but you paid 8 Groschen and 8 Pfennigs more for that product than I did, a losing proposition. If you do the latter, I simply wait until you run out of money from living expenses, which will happen to you first because you paid into the trinket fund and I didn't, so I have more money remaining. I then buy up your share at the bankruptcy auction and cackle evilly.