As I said last time, I have been working on an urban crawl in my sandbox. It becomes a fight between my wont to add all kinds of details and hooks and the need to keep things loose for improvisation. One detail I did add was that each tavern and inn now has a chance that someone robs the PCs while sleeping, and the truly scummy taverns and inns also have a chance that the PCs get a disease.
How this works is that if the PCs stay in a tavern at night (which they usually do), I roll three dice and compare to a number, like a frequency of appearance, with 6 being normal. Inns, which have rooms, might be a 3; scummy taverns a 9; sleeping on the street a 12. That's why inns are pricier for a stay. If one shows up, a cutpurse (GURPS Dungeon Fantasy 10: Taverns, p. 6) picks a PC at random to target first. He gets +10 against a sleeping target, but is going for money, which is presumably in an inner pocket or something, so -5 there, making his effective Pickpocket skill 17 vs. the higher of the PC's Perception or Streetwise skill. Success on the Quick Contest means he gets the PC's money; critical success means he also gets his gems, if any, which are presumably better guarded and less expected. Critical failure wakes the PC. The cutpurse moves from PC to PC until he loots them all or he wakes one. They're not going to go for big items like magic swords, which are harder to steal and lug off without someone seeing it, so some PC items are safe.
In a truly scummy tavern, the bedbugs might bite. The chance for this in a scummy tavern 3 or less on 3d, or 6 or less on the street. If one bites, it might spread the Aching Ague or an akin disease if the PC fails his HT roll. Remember to apply the Hygiene modifier of the settlement (GURPS City Stats, p. 6) to the HT roll. If you don't know it, set it to 0 in a village or to -1 in a bigger settlement, like a town or a city.
Bedbugs spread it, or rats and fleas on the street.
Statistics: Blood Agent (Bedbug bites); HT to resist; 1d-2 day delay; 1d-4 HT damage; 12-hour cycle with 6 cycles. Symptoms produce stomach problems, which is the Nauseated condition (p. B428) after losing 1/3 HT; after losing 2/3 HT, doing anything stressful like combat or moving more than 1 yard a second means a Retching (p. B429) spell for 2d seconds; resist HT to keep from retching. Not contagious.
Slumming it a longer layoff gives a flat chance of robbery. While GURPS Dungeon Fantasy murder-hobos are specifically mentioned as not being able to have Status lower than 0 (Pyramid #3/58: Urban Fantasy II, p. 13), they can try to live like hobos who do not murder anyone. Living at Status -1 gives a robbery on 12 or less on 3d, and a disease a 6 or less, but costs only $75 a week. Living at Status -2 gives a robbery on a 15 or less on 3d, and a disease on 9 or less, but costs only $30 a week. Living at Status 0 or better gives plot immunity from robbery or disease during layoffs. Think of it as making enough extra money to cover any robberies. If someone suffers the aching ague during downtime, just rule he starts the game down 1d HT.
Oddly enough, the murder-hobos at our table won't come into contact with these rules unless something truly bad happens, as Yémos always casts the Watchdog spell before going to bed.