Eh, I'll just copy and paste the list:

Pokémon

- Mew
- Shinies
- High-IV pokémon

Items

- TM Stealth Rock
- TM Grass Knot
- TM U-Turn
- TM Charge Beam
- TM Stone Edge
- TM Trick Room
- TM Explosion
- D/P evolution items (protector, dubious disc, etc.)
- Liechi Berry
- Landsat Berry

If you don't have any of those, though, pretty much anything interesting is fine.