The explosive processing and nucleosynthesis in the ejecta gives rise to a large fraction of the present day element abundances. Explosive nucleosynthesis calculations require the knowledge of nuclear reaction rates at high temperatures, to a large extent for unstable nuclei, based on theoretical or experimental efforts. The comparison with abundances from specific supernova observations can probe the correctness of the stellar evolution treatment and the 12C( O rate. SN 1987A showed reasonable agreement with C, O, Si, Cl, and Ar abundance observations. Supernova remnants make it possible to compare with the observational results from optical, UV, and X-ray observations. The delay time between collapse and explosion via neutrino heating determines the amount of accreted matter onto the proto-neutron star. Combined observations of the ejected 56Ni, as deduced from the 56Co powered supernova light curve observations, the 57Co/56Co ratio from gamma-ray observations (possible in SN 1987A) and the amount of 44Ti (possible in Cas A) would give unique information on the position of the mass cut, the energy of the shock wave and the neutron/proton ratio in the innermost ejecta . The very innermost layers of the ejecta, driven off the surface of the nascent, cooling neutron star and heated by a strong neutrino flux, might also include r-process nucleosynthesis, based on the built-up of heavy elements up to Th and U via rapid neutron captures. Provided that r-process conditions can be obtained , neutron densities and temperatures well in excess of >1020cm-3 and T>109K result, which cause reaction timescales as short as s, while the beta-decay half-lives of the involved nuclei are longer, roughly of the order of 10-1 to a few 10-3s. This approaches an - equilibrium and a capture path on contour lines of constant neutron separation energy in the nuclear chart. Only a few nuclei along the magic neutron numbers 50 and 82 are know in the regime of neutron separation energies between 2 and 4 MeV. A full understanding requires a highly increased amount of data and nuclear structure knowledge far from stability, i.e. masses, half-lives, possibly neutrino interaction cross sections and level densities and giant resonance properties to predict gamma widths  for the reaction rate calculations. The question whether shell closures are quenched for nuclei far from stability is here highly relevant and enters in an important way in the abundance features. Astrophysical uncertainties include the major question about the obtained entropies and n/p ratios in this matter and whether this material is finally ejected or hindered by fall back, due to reverse shocks in the ejected envelope.