Hey Kat!
Packing takes practice. I luckily had a job that required me to live two weeks on the road, so I got very good at packing! Honestly though, you might want to practice before hand and figure out what you need vs want. Having said that, it's your wedding - if it's going to stress you out more leaving something behind, bite the extra baggage checking costs. I'm not bringing OOT or anything of that stuff, so that makes things easier. I'm getting married in November 2014, and we sent out our STDs in May of this year. We aren't planning to do formal invites until the New Year, once we have a travel agent and quote locked in. This was a big debate because we need the quote beforehand, and it's only valid for 30 days... But for the most part we are in constant communication with our guests anyways, so they will all know what's up which is nice. We debated sending out invites first but we really wanted to list all the travel agent and flight information in them.