Front and rear lights
Being seen, and being able to call someone.
What a plan says about it
The planner writes this from the ride you describe, so there is no version of it that is true for everybody. Here it is worked against one ride, named below, with a single answer changed at a time to show what moves.
2 nights · wild camping · cold but not freezing (8 °C) · gravel and tracks · towns daily
Not optional even in summer. Days end earlier than planned and the last hour is the one that goes wrong.
On that ride the planner marks it essential.
Ways to satisfy it
One object doing one job, so this is a choice between them rather than a shopping list. Every one carries what it costs you as well as what it gets you.
Rechargeable USB lights
Cheap, bright, and they move between bikes.
but One more thing to charge, and the cold shortens the runtime.
A plain web search. We earn nothing from it.
Find one ↗Dynamo hub and light
Never charged, never thought about, never flat.
but Costs a wheel build, and it is weight you carry in daylight too.
A plain web search. We earn nothing from it.
Find one ↗
Where to look
We hold measured dimensions for bags and for nothing else, so this hands the requirement to a search rather than picking something for you. Nothing on this page has a price, a weight or a maker attached to it, because none of those were measured.
A plain web search. We earn nothing from it.
Search for Front and rear lights ↗Which one do I need?
That depends on the ride, and this page does not know it. The interview does, and it is the only thing here that can answer the question — no account, and every line it gives you names the answer that produced it.