High-style sportswear, cotton slacks and walking shorts, and plenty of colorful sundresses are the palette of clothing you'll see in PV. Bring lightweight sportswear, bathing suits, and cover-ups for the beach. In addition to shorts, pack at least a pair or two of lightweight long pants.
Men may want to bring a lightweight suit or slacks and blazers for fancier restaurants (although very few have dress codes). For women, dresses of cotton, linen, or other lightweight, breathable fabrics are recommended. Puerto Vallarta restaurants are extremely tolerant of casual dress, but it never hurts to exceed expectations.
The sun can be fierce; bring a sun hat and sunscreen for the beach and for sightseeing. You'll need a sweater or jacket to cope with hotel and restaurant air-conditioning, which can be glacial, and for occasional cool spells. A lightweight jacket is a necessity in winter, and pack an umbrella, even in summer, for unexpected rainstorms.
Bring along tissue packs in case you hit a place where the toilet paper has run out. You'll find familiar toiletries and hygiene products, as well as condoms, in shops in PV and in most rural areas.