Hi roxfox,
Good question! There are certain STIs that may be spread from person to person through skin-to-skin contact - HSV 1 and 2, HPV/genital warts, pubic lice, - and HSV 1 can also be spread through kissing/saliva as an oral infection.
(Check out
Can I Get Pregnant, or Get or Pass On an STI From That? for a detailed breakdown).
But, this is a lot lower risk relative to something where sexual fluids are involved (like oral, anal, or vaginal sex). So if you just met someone at a party and you wanted to kiss and/or touch them with clothes on, your risk would be very little in terms of exposing yourself to STIs. (Although you can potentially catch a cold/flu/virus from exposure to someone else's saliva, most people tend to call that risk worth it!)