as you say, depends on when, where and how long
- deep winter, up high/real mountains for a couple of days - normal camping kit plus a light set of (dry) spare clothes (eg socks/running troos/longsleeved tee shirt), 1 day more food than needed and spare fuel for stove than required
- deep winter for a day up most places - tarp, stove, plus extra food than required for the day
- 3-season outside of winter, up high for couple of days - as deep winter but probably just spare socks
- 3-season for a day most places - as deep winter day but lose the stove
other than that, a good mobile phone (ie provider), a credit card and a sense of humour