If you have lived your whole life in a tropical climate, packing for a European spring is genuinely difficult to judge. Ten degrees sounds mild written down. Standing on a platform in Lucerne at seven in the morning, it is not.
The principle is layers, not bulk. A thermal base layer, a fleece or thick jumper, and a windproof outer shell will handle everything from Amsterdam in April to a glacier at Titlis. One enormous coat will leave you sweating indoors and still cold outside.
Footwear is the thing people get wrong most often. You will walk far more than you expect, five to eight kilometres on a city day is normal. Bring shoes you have already broken in, and a second pair in case the first gets wet.
The two forgotten items: a universal travel adaptor, and gloves. Both are cheap at home and irritatingly expensive to buy in a European tourist district.
One last note, cabin baggage allowances are enforced far more strictly on European carriers than most travellers expect. Weigh your bag before you leave.
