2d- erratic fellow loses head over wager (9) - H???A???D - must be haphazard , but can't see the wager bit
9ac- seems to be the last place you would visit (6) - N???E? - if haphazard is right, then 3rd letter here is "p", so Naples would fit, but don't see why
15ac- ancestral hall on River Bank, not found in Ireland (4) - T??? - 3rd letter is "a" if haphazard is right, in which case toad (of toad hall) would fit but how does that relate to river bank and Ireland?
27ac- prodigal son's gloom about death (8) - S?E?D??? - seems like it must be something to do with spending, but don't see how gloom and death are in the answer
26d - a Russian, say, has to toil endlessly (4) - ???V