Phones get used more heavily on summer trips, constant photos, navigation, and cranking up screen brightness in the sun all drain the battery faster than usual. Packing at least one mid-capacity power bank, in the 10,000-20,000mAh range, is a smart precaution.
Charging a phone directly under the sun puts both the device and the battery at risk; with ambient heat already high, the extra heat generated during charging can cause lasting performance loss. Charging in the shade or indoors whenever possible is the safer move.
In humid environments like beaches or poolside areas, cables and adapters coming into contact with water create a real short-circuit risk; carrying them in a simple waterproof bag or pouch is an easy but effective precaution.
If multiple people share a room, one multi-port GaN charger takes up far less space than everyone bringing their own adapter, and makes much more efficient use of limited outlets.
For short daytime excursions, a small solar backup charger might sound appealing, but their real-world output is usually low, so a properly sized power bank should always be the reliable backup, not a solar gadget.