The characters will find some treasure during adventures. Many monsters like to accumulate treasure hordes. There are also lost hordes in old ruins. I also like to pay characters for adventures, if they're working for someone wealthy enough to afford it. One of the main differences between the PCs and NPCs IMC is that the PCs are independent agents who are free to work for various groups and powerful individuals. Most NPCs are retainers of one group or another.
There is usually quite a bit of down time between adventures IMC, so characters often have jobs they do between adventures as well. Bodyguard, teacher, sell sword, priest and thief have all been pitched by the players as professions for the characters. One of the characters works in his family's pastry shop when not adventuring (as a sous chef, since he spends too much time adventuring to really master those fancy sugar sculptures).
The characters are usually too cagey to become too closely tied to a single patron.