For FOSDEM first-timers, it's good to wear the shoes that work best for a lot of standing and walking and can handle rain and some puddles (depending on the weather). These might not be the best looking shoes you have (or they might be) it just needs to be something that once you put on you won't have to think about until you take them off, which will probably be hours and hours later. I am bringing two pairs with very different weights and support styles to switch between.