This may work:
Cases[x[i][t]^3*y[k][t2], a_[i_][t_]^n_. :> Table[a[i][t], {n}], 1] // Flatten
This works, thank you very much!
This almost does the job, but I would need terms like (x[i][t])^3 to be recognized as three different x[i][t] items in the output list!
Perhaps you can do it with Cases and a pattern:
Cases[x[i][t]*y[k][t2], (x | y)[i_][t_], All]
