A few things that have been super useful for me, portable charger (absolute lifesaver), a small first aid kit, and a refillable water bottle. Offline maps are a must, especially if you’re exploring places with spotty service. I also always make sure I have an eSIM ready before I land, Jetpac has been solid for that, especially since I don’t have to deal with finding a SIM card on arrival.
Oh, and a good book or a journal! Solo trips always come with unexpected downtime, and it’s nice to have something to unwind with