A few things I like, though not all of them are strictly needed:

    long long foo; /* bigger ints on 32-bit platforms */
    uint32_t bar;  /* stdint.h, integers of specific bit width */
    int array[n];  /* length-n array, where n is a variable */
    for (int i = 0; i < n; i++) /* loop-local variable */

Also, the safer stdio functions like snprintf.