To have a travel umbrella never hurts, especially during the rainy season in Milan.
Ear Plugs might be of help to light sleepers because Barcelona is a noisy city. There are people on the streets in the early morning hours largely due to the fact that city’s nightlife starts and finishes late for locals (and tourists alike).
To obtain Euros in advance is useful for paying for small items, gifts and food with cash, if desired.
Medical Supplies are not needed during the stay in Milan. It is always cheaper to buy local brands. However, all prescription medications for allergies and other diseases of certain brands are a must-bring.
A pair of dark sunglasses and scarves should be always in hand no matter it comes to a walk around the city or doing the shopping.
A trendy bag and purse for all necessary belongings and documents are a must. They must always be held in front because of the numerous pickpockets everywhere, especially in tourist spots and on the metro.