BAGGAGE, Checked, carry on and what to pack.

For international travel there is no standardized rule about size, weight and cost of a checked bag.  All rules are specific to the airline with some common guidelines.  Its best to check with your airline to see what their bag policy is before you complete your packing.   When you depart North America for Europe, you will be checking your bags through to your final destination even if you are connecting to a smaller inter-European airline that has a different and more restrictive bag weight policy.  However if you are making a side trip before or after the convention within Europe you need to be aware of that airline's checked and carry on bag policy.  Delta, for example, does not charge for the first bag on international flights which is surprising since they charge $25 for a one way domestic flight.  From the US, the bag may weigh up to 50 lbs without incurring an overweight or excess baggage charge.  Most European carriers allow 20 Kg (44 pounds) and charge 25 Euro per checked bag.  Please note that the extra few pounds Delta allows might later incur a charge say on SAS or Baltic Air.  I say "might" because you may get away with a few extra pounds but be prepared to either pay the extra fee or pull heavy items out of your suitcase to stick in a carry on back pack or purse.  I have a small colapsable cloth bag (like a big launry bag with a zipper) that I carry in my suitcase.  If I start to run over on weight, I have used this as a second checked bag paying the 25 Euros rather than the penalty for excess baggage which can be 5 or more Euros per kilo.  Your second bag then can also be up to 20 Kilos.  This might be helpful if you are inclined to bring home lots of souvenirs.

Most airlines allows customers to bring one carry on bag and one personal items such as a purse, backpack or laptop bag. 

Be mindful of some of the discount European carriers who may have a cheap fare but charge more for luggage and have a lower weight allowance.  (e.g Ryan Air)
Make sure your luggage is tagged.  I have never lost a bag permanently but a few times over a lifetime of travel I have had to wait a day or two to have a bag delivered.

I prefer a hard sided suitcase that can take shocks and not damage anything inside.  Soft sided bags are fine but just be sure and wrap fragile items in clothes.  Except your meds, most anything can be easily secured in Tallinn.  The main convention hotel is adjacent to the city's biggest indoor mall complete with drug and department stores. 
Most of the sessions at the convention are summer casual.  Slacks and sports shirts for men will be standard. The installation banquet is business casual with coat and tie for those being installed so there's no need to pack an assortment of suits.  Men, you can easily plan to pack a blazer or sport coat and wear it on the plane and dress it up as needed during the convention.

Try to resist over packing.  Laundry services are readily available and housekeeping can bring an iron to your room.

The European division is also asking convention visitors to bring one or more articles of lightly used clothing for the Raake Civitan Club"s clothes closet for the poor. This might be a way to lighten your load and make room for souvenirs for your trip home.