Probably just a voltage regulator, a clock source, reset pin logic, a couple ROM chips (2 8-bit wide chips or 1 16-bit wide), some static RAM, a PAL/GAL/74xx logic for address decoding and chip select pins, stuff to deal with the multiplexing, and whatever input/output you want (bus buffers for parallel I/O, off the shelf UART chips, etc)

I’ve only done it with the 6502 and Z80, but the 8086 shouldn’t be too much harder. There are plenty of resources available online for those two chips that you could adapt!

In minimum mode you don't need more than a ROM, SRAM, and clock source.