Im pretty new to the Fuji system but Im very satisfied with the X-S20 so far. Since youre going to Japan, Id definitely prioritize reliability and safety for your gear. I dont like charging inside the camera because Im worried about the battery overheating or the port getting loose. These are the basics that have worked well for me:

• Fujifilm BC-W235 Dual Battery Charger
• Fujifilm NP-W235 Li-Ion Battery
• Peak Design Everyday Sling 6L The sling fits the deep grip nicely and I have no complaints about the protection it offers. I wouldnt skip the tripod entirely even with the IBIS. I use a Manfrotto PIXI Mini Tripod because its sturdy and small. Better to have it and not need it than to get blurry shots at night.

Like someone mentioned, internal charging is efficient. The X-S20 supports USB-C PD. If you use an Anker Nano II 45W USB C Charger, it charges the NP-W235 fast enough to skip a dock. Since the IBIS is rated for 7 stops, maybe just pack a K&F Concept 62mm Variable ND Filter for long exposures. FujiRumors has some great compatibility lists for PD power banks if you want more data.

I'm very satisfied with my X-S20. Saw this earlier but just now responding... whats your plan for storage? Im always cautious about card errors on big trips. I've compared these two:

• SanDisk Extreme Pro 128GB UHS-I V30 SDXC: Very reliable for photos, tho its a bit slow for the 6K video modes.
• Lexar Professional 1667x 128GB UHS-II V60: Much faster for the high-end video recording this camera does. Both have worked well with no complaints.