You need a table that can become any table you need, on the fly.
Remember the table I used for random NPC names, which was built on a mnemonic cypher used by Lewis Carroll? Here's a compressed version:
|1 - A, B, C||4 - O F Q||7 - Oi, M, P|
|2 - E, D, W||5 - U, L, V||8 - Ei, H, K|
|3 - I, J, T||6 - Au, S, X||9 - Ou, G, N|
|0 - Y, R, Z|
You can use it to suggest the first letter of a word, if you only know the category you're looking for. For example, you ask the 1st level thief in our example, "What area of town are you in?" If the thief is in the merchant's quarter, you want to know what the merchant trades in: roll a d10, pick a word for a precious object that starts with the appropriate letter. Rolled a 7? You want something that starts with an M, a P, or the Oi dipthong. Oils! Or exotic papers! Or pearls! Or ornate masks! If you find one letter isn't enough, you can roll two dice to get an abbreviation: adjective + noun. Rolled a 46? It's the house of a quilted shirts merchant, or a feathered serpent merchant... or you can interpret the two digits as two letters in one word... F X might suggest a dealer in fox furs.
If you need to think up a whole table on the spur of the moment, this one table can take the place of any other.