What to wear to a wedding? Also, what makes a good wedding gift?

It’s not about what is worth what. To be honest Whitey’s wedding this weekend is the first wedding I’ve ever been to since I was like 4. The formalities of such an event are completely foreign to me. I just didn’t want to make an ass out of myself… but knowing the guest list there is .000001% chance that anything I could or would do will be top 25 things that will be remember from this wedding. PSK FTW.