One solution to finding wood is a rolling program of ringbarking trees to enable a steady source of wood throughout the year. There would also have been opportunities to obtain storm-wood from the local rivers and even from beaver dams.
From the archaeology we can see that nuts were popular but a lot of the diet would presumably have been meat.
If time is spent between the summer camp and the winter camp then folk would have know the location of the best food larders. The folk at Star Carr also took fish and wildfowl. So I still don't think that they would have spent hours foraging for fruit & veg especially when meat was so plentiful & relatively easy to obtain.

"As Tombo says a big camp fire will burn a lot of wood in one evening."

Without wanting to get embroiled too deeply in a guesstimating competition, I'm nonetheless interested in the idea of necessary/usable energy expenditure, and how our ideas today reflect our own lifestyles, in that we can impose those upon our ancestors.

We now have Big Camp Fires, recreational fires, the 'white man's fire' which gives us enough blistering heat and blinding light to drive back the demons in our mind and make the forest 'retreat' a good 30 feet or more.

A 'good' fire is a small smouldering heat used principally for cooking or to heat an opening so that the chill is taken off the air. We have adapted to central heating (I say 'we' I'm sure there's plenty of you like me who can't stand the excoriating moisture-sucking abomination) and likewise have a hard time imagining people in Northern Britain not needing a big fire all night long.

Gathering:

Children love gathering firewood, and myself as a Woodcraft leader witnessed a gaggle of 10 year olds bringing back more wood in three hours than we would have sensibly burned in three days. I can happily gather wood for hours, and never feel cheated, one always learns something new about the woodland, or own abilities, when gathering wood. To me it's the perfect kind of meditative state, gathering wood.