:up: ... when 'excursion' is used to mean a trip. If the context makes 'excursion' into a sort of metaphor meaning 'the part of the activities devoted to going on a trip' then 'for' is possible (but 'go for' is a prepositonal verb, unlike the phrasal verb 'go for' that means 'choose'):
'I'm going for the excursion, but I can't stay on for the party in the evening.'
b