Among other picks:
OKC has Miami's 1st round pick in 2021.
Rockets 1st round pick in 2021
Hawks 1st round pick in 2022 (top 14 protected)
Clippers 1st round pick in 2024 (by then, George and Kawhi may be long gone)
Rockets 1st round pick in 2024 (by then, Houston may have substantially regressed)
Clippers 1st round pick in 2026 (see above)
Rockets 1st round pick in 2026 (see above)
In addition to those picks, the Thunder have their own first round pick each year; the Nuggets first round pick next year, the 76ers 1st round pick next year (top 20 protected) and several other years when they can force either or both the Rockets or the Clips to swap their first round picks.
In all, OKC has the rights to 18 first round picks between now and 2026. Not all of the picks are equivalent to 2nd round picks.