My challenge to you is to discover a new theme from your personal experience that can be expressed through our Scouts on Stamps hobby. Go beyond the traditional categories to invent a concept that has significance to you. Find a particular area of special interest, maybe something relating to your own Scouting experience, and start enjoying the search.
Pick a particular Scout subgroup (Girl Scout Stamps or Black Scouts on Stamps) or a country or region (Scout Stamps of Canada or Scout Stamps of Latin America). Try a special time period (Scout Stamps Issued While I Was a Scout, or The Second 40 years of Scout Stamps), or a thematic approach (Campfires on Scout Stamps or Scout Buglers on Stamps).
Perhaps a noteworthy event (Stamps Honoring the 75th Anniversary of Scouting or Philately of the 17th World Jamboree) or a series of events (National Jamborees of Australia or the Pan Arabian Jamborees). Possibly a favorite type of stamp emission (Scout Stamp Souvenir Sheets or Airmail Scout Stamps) or a famous Scout personality (R.Baden-Powell on Stamps or Paul Siple Scout Covers).
Maybe a choice of usages (Scout Stamps on Commercial Covers or Scout Stamps on First Day Covers), unusual usages (Scout Stamps on Postage Due Covers or Scout Stamps on Censor Covers), cachets (Scout Campsite Cachets or Scout Athletic Event Cachets), postal markings, cancellations, perfins, etc.
What you collect is completely up to you. It is not important that the material be rare or expensive. Conducting and publishing research on your stamps may turn the average item into a valuable specialty. Come up with an idea that unifies some aspect of Scout Philately and allows you to express yourself. Don't be constrained to filling boxes on preprinted pages or abiding by what others think is a Scout issue. Let your imagination be your only guide. Good luck and happy collecting!