The trolley tour of Boston, offered as an optional, is the best way to see the entire city. Take it at your own pace, but I would suggest stopping off at the USS Constitution and Fenway.

ankopsu Article on Boston

Christmas Markets in Vienna are great. Buy some mulled wine (Gluhwein in German)which is served hot and is quite spicy. The mug it comes in is yours to keep - a great souvenir -but if you don't want it return it and get your €2 deposit back (Pfand).

Mike Contiki Article on Vienna

If you are doing a time out tour (staying in hotels), a travel iron/hairdryer will come in handy as many european hotels do not provide these facilities.

Vicki - Contiki Staff, Europe Article on Suggested packing list - Europe - Summer