“Minimal” means that racket/kernel includes only forms that are built into the Racket compiler and only functions that are built into the run-time system. Currently, the set of bindings is not especially small, nor is it particularly well-defined, since the set of built-in functions can change frequently. Use racket/kernel with care, and beware that its use can create compatibility problems.
The racket/kernel module exports all of the bindings in the grammar of fully expanded programs (see Fully Expanded Programs), but it provides #%plain-lambda as lambda and λ, #%plain-app as #%app, and #%plain-module-begin as #%module-begin. Aside from #%datum (which expands to quote), racket/kernel provides no other syntactic bindings.
The racket/kernel module also exports many of the function bindings from racket/base, and it exports a few other functions that are not exported by racket/base because racket/base exports improved variants. The exact set of function bindings exported by racket/kernel is unspecified and subject to change across versions.