If stoping by the post office, pick up some of those nice, Tyvek flat rate envelopes and equivalent stamps. At your leisure, stamp and self-address the envelopes. Now, before your next big conference or vacation, grab one of the envelopes and pack it, they are very lightweight and foldable so easy to accommodate even if you are a travel light kind of guy like me. At the conference, feel free to pick up as much schwag, marketing muck, and business cards as you can fit in the envelope and drop it already stamped and self addressed in a post box or the hotel front desk. It will be back home to you in a day or two and you saved yourself from having to carry it back.
(This hack was inspired and refined by my Dad, who is one of the smartest travelers I know.)