  The composition of hot and dense nuclear matter is calculated including the
$1p$-shell nuclei $4 \le A \le 16$. In-medium shifts, in particular Pauli
blocking, are determined by the intrinsic wave function of the nuclei. Results
are given within a shell-model approach for the nucleon wave function. Light
nuclei are not always well described by the shell model. The 'clustered'
nucleus $^8$Be exhibits strong correlation effects because of $\alpha$-like
clustering. Intrinsic cluster structures are also significant for the nuclei
$^6$Li, $^7$Li, $^7$Be, and $^9$Be. The contribution of the relatively rare
elements Li, Be, and B, to the equation of state (EoS) of matter near the
saturation density is overestimated in simple approaches such as the nuclear
statistical equilibrium (NSE) model. Both, the treatment of continuum
correlations and the account of in-medium modifications are considered for the
contribution of $^5$He and $^4$H clusters. Compared to the extended NSE
including unstable nuclei, the contributions of the corresponding P$_{3/2}$
channel with $A=5, Z=2$ and P$_{2}$ channel with $A=4, Z=1$, respectively, to
the EoS are strongly suppressed at high densities owing to Pauli blocking
effects. For the shifts of the binding energies of the light $p$-shell nuclei,
simple fit formula are given to calculate the composition of hot and dense
matter in a wide parameter range.
