The Swiss Travel Pass earns its price

Buy it. The 8-day pass covers every train, boat, and most cable cars on this itinerary. Jungfraujoch and Titlis are the only big paid extras. Without it, individual tickets add up to roughly twice what the pass costs, and the convenience of skipping every ticket window is worth it on its own.

Cloud is the variable, not rain

Jungfraujoch at 11,000 ft is brilliant in sun and a white-out in cloud. Same day, different hour. Move the high-altitude excursions to whichever morning the forecast looks clearest; everything else (Lucerne, Interlaken, Zurich old towns) reads fine in any weather. Check meteoblue the night before, not the week before.

Fondue is for cold months; raclette is for any month

A cheese-fondue dinner in June feels like overdressing. Order raclette instead. Same Alpine cheese tradition, melted off a half-wheel against new potatoes and pickles, eaten in any temperature. Or save the fondue for one specific evening at altitude (Schynige Platte, Männlichen) where the cold does the work for it.