Be seen when at anchor!
In crowded anchorages, in poor visibility and with some backgrounds a mast head anchor light is easily missed by someone manoeuvring and looking ahead rather than up, so a low level light is a good idea shown alone or with a masthead light. And if they have LED bulbs the drain on the battery will be little.
A traditional oil lamp may not meet modern standards but one would make a good low level light used with the mast head light.
In restricted visibility, especially when close to a channel, a busy harbour or when anchored in an unexpected place leaving an AIS transceiver on is a good idea, at least some vessels will be able to see you.
And don’t forget the radar reflector if it is not permanently hoisted, the black ball daylight symbol and if installed the active radar responder in bad weather.