If $\lambda$ is an eigenvalue of $A$, then $\lambda^{100}$ is an eigenvalue of $A^{100}$.
So the eigenvalues of $A^{100}$ are :
$(-1)^{100}=1$, $1^{100}=1$, and $0^{100}=0$.
Hence the eigenvalues of $A^{100}+I$ are :
$1+1=2$, $1+1=2$, and $0+1=1$.
Therefore,
$|A^{100}+I|=(2)(2)(1)=4$
Answer : $\boxed{|A^{100}+I|=4}$