  Parking functions are a widely studied class of combinatorial objects, with
connections to several branches of mathematics. On the algebraic side, parking
functions can be identified with the standard monomials of $M_n$, a certain
monomial ideal in the polynomial ring $S = {\mathbb K}[x_1, \dots, x_n]$ where
a set of generators are indexed by the nonempty subsets of $[n] =
\{1,2,\dots,n\}$. Motivated by constructions from the theory of chip-firing on
graphs we study generalizations of parking functions determined by $M^{(k)}_n$,
a subideal of $M_n$ obtained by allowing only generators corresponding to
subsets of $[n]$ of size at most $k$. For each $k$ the set of standard
monomials of $M^{(k)}_n$, denoted $\text{stan}_n^k$, contains the usual parking
functions and has interesting combinatorial properties in its own right. For
general $k$ we show that elements of $\text{stan}_n^k$ can be recovered as
certain vector-parking functions, which in turn leads to a formula for their
count via results of Yan. The symmetric group $S_n$ naturally acts on the set
$\text{stan}_n^k$ and we also obtain a formula for the number of orbits under
this action. For the case of $k = n-2$ we study combinatorial interpretations
of $\text{stan}_n^{n-2}$ and relate them to properties of uprooted trees in
terms of root degree and surface inversions. As a corollary we obtain a
combinatorial identity for $n^n$ involving Catalan numbers, reminiscent of a
result of Benjamin and Juhnke. For the case of $k = 1$ we observe that the
number of elements $\text{stan}_n^1$ is given by the determinant of the reduced
`signless' Laplacian, which provides a weighted count for $|\text{stan}_n^1|$
in terms generalized spanning trees known as `spanning TU-subgraphs'. Our
constructions naturally generalize to arbitrary graphs and lead to a number of
open questions.
