A good travel kit should feel edited, not impressive. The goal is to bring what you are likely to use and leave behind the stuff that only makes the bag more annoying.
Quick answer
For most people, a good travel kit is one storage bag or case, one compact grinder if needed, one small maintenance pouch, charging gear only if necessary, and as little loose equipment as possible.
Start with the storage
If the bag or case is wrong, the rest of the kit gets messy fast. Good travel storage does more than most extra accessories.
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Only bring the grinder if it earns the space
Compact grinders make more sense for travel than full home-style setups. If you do not need it, do not pack it.
Keep maintenance light
Travel maintenance should be the basics only. Bring what solves likely problems, not a drawer's worth of backup tools.
Watch the charging clutter
Charging gear expands quickly. Bring only what you clearly need and keep it contained.
Bottom line
The best travel kit is the one that stays compact, easy to pack, and easy to put away once you arrive.