a cache of old photographs in a trunk
There are also some stories that are very much in both camps. 'Lorelei of the Red Mists' by Leigh Brackett and Ray Bradbury (literally, one half was written by each writer- and it's damn hard to tell where they switched over) starts as a very Planetary Romance type tale, with a interplanetary thief escaping into hidden territory while being chased by the Patrol, and ends up in a very Sword & Planet place, which if it didn't reference the protagonists initial motivation at the end of the story, might as well have been Sword & Sorcery (not helped by the fact that one of the characters is called Conan- although his character was apparently nothing like the more famous barbarian).This quote from there seems useful:
I'd say that you'd know both terms when you see them (for example any story in which a modern day Earthman travels by some complicated means, either scientific, magical or unexplained, to a different planet (generally by mentral transference)- is certainly Sword & Planet. Any story in which a far-future space adventurer gets caught up in the intrigues of an alien society is Planetary Romance. And then there are stories like the Sea Kings of Mars where a tomb robber from a far-future Mars gets magically transported back to Ancient Mars, which blur the edges again.