Polished loafers are often dressy enough. Look for crepe or Vibramsoles, rather than leather. Make sure they are comfortable. You'll be glad you have them in those youth hostel communal showers. Bring one to three weeks worth, since laundry may be expensive.
Wool socks are especially important in non-tropical climates.
Women may want to bring along a couple of pairs of tights. Bring at least one wool and one cotton. Wear one while traveling to save space. Pack a couple if you like wearing them. Bring at least one to three weeks worth, since doing laundry is often expensive.