What are the materials needed to make a nuclear weapons?

At a minimum:

• Fissile material to provide the energy
• Conventional explosives to rapidly assemble (about 1ms to 10ms) the fissile material from subcritical to supercritical form
• A tamper made of dense metal to contain the reaction for about 1µs to get good yield
• neutron sources to start the fission at optimal supercriticality

To make a practical bomb additional materials and systems would be required.