you might have your thin cat checked for worms - we've got one my hubby rescued from a dumpster as a starved feral kitten - he's smaller than most cats, and always slim. he's an outstanding hunter and eats much of what he kills, but probably because of that he does get worms ... we watch to see if he's losing weight, and if he is, we check. he needs to be wormed several times a year to keep healthy weight on. interestingingly, our other hunter doesn't seem to have as big a worm issue and keeps weight on just fine year round. as a rule, if one's got worms, they probably all do, but different individuals seem to have different ability to defend against them, or keep the worm load down enough to not show anemia or weight loss.
anyway, it's not something that needs to be done for the weekend, but might be worth looking at after you get back.