If you are traveling to Poland for the annual Science Fiction Research Association conference in July, you may want to follow some of the advice on OneBag.com by Doug Dyment for lighter baggage tips:
Theres no question: overpacking tops the list of biggest travel mistakes.Thus this Web site, which offers exhaustive some might say exhausting! detail on the art and science of travelling light, going pretty much anywhere, for an indefinite length of time, with no more than a single carry-on-sized bag.
Dyment offers lots of advice including making a list, avoiding unnecessary duplication, and reflecting on the purpose of your travel (i.e., each trip requires different supplies). He provides many sample lists and tips on his site that you may find useful.
via Leisure / Business Travel Packing List – Travel Light One Bag!.