I've written various handouts for math training camps at the national level. As you might be able to guess, I really like geometry. The following are meant to be comprehensive notes while the next section contains problem compilations.

Handouts

• Functional Equations Over Reals - 2024 Canada EGMO Training
  Important ideas for tackling real FEs.
• Real Polynomials - 2024 Canada Winter Training
  All the tools you'd ever need for polynomial problems.
• Projective Geometry - 2021 Canada Summer Training
  Basics on projective geometry.
• Ratio Chasing - 2021 Canada Winter Training
  Powerful applications of Ceva's, Menelaus's, and Law of Sines. Still counts as synthetic.
• A Few Configurations - 2020 Canada Winter Training
  Around the orthocenter, incenters and excenters, and isogonal conjugates.

Compilations

• A Few (Geometry) Problems - 2021 Canada Summer Training
  A few interesting problems with a different flavour from olympiad geometry.
• Incircles - 2021 Canada Summer Training
  Some simple facts about incircles and some not-so-simple problems about incircles.
• Complete Quadrilaterals and the Miquel Point - 2021 Canada Summer Training
  A closer look at a general configuration. Please let me know if you solve C7.
• Functional Equations in Number Theory - 2020 Canada Summer Training
  A compilation of problems involving FEs in NT.
• Polynomials in Number Theory - 2020 Canada Summer Training
  A compilation of problems involving polynomials in NT.
• Weird Geometry - 3020 Canada Summer Training
  A grim prediction of olympiad geometry 1000 years in the future.
• (Real) Functional Equations - 2020 Canada Summer Training
  A compilation of problems involving FEs, mostly concerning R.
• Tangent Circles - 2020 Canada Summer Training
  TL;DR either use inversion or look for a Miquel point. Sometimes both.