I am thinking of something like glib , but perhaps in a thin version with a minimal footprint. This requires basic utilities such as linked lists, vectors, and hash tables. It should also have a minimum runtime.
Not really a library, but a tested, optimized and documented piece of code: sys/queue.h on * BSD and Linux systems have macros for various types of intrusive linked lists and queues.
sys/queue.h
uthash is a good hash table (full of macros), it also contains a linked list, a dynamic row, and dynamic array macros.
I also highly recommend sys/queue.h (suggested by larsmans) for simple and well-tested linked lists.