you can manually insert extra files in scenario pack

src/fileio/fileio.hpp

@@ -40,6 +40,10 @@ fs::path os_file_picker(bool saving);
 extern fs::path run_file_picker(bool saving);
 
 const std::set<fs::path> save_extensions = {".exg", ".boe", ".SAV", ".mac"};
+
+// Extra files you can package with a scenario
+const std::vector<std::string> extra_extensions = {".sav", ".txt", ".rtf", ".htm", ".html", ".exg"};
+
 // Return a directory's files sorted by last modified time
 std::vector<std::pair<fs::path, std::time_t>> sorted_file_mtimes(fs::path dir, std::set<fs::path> valid_extensions = save_extensions);
 

src/game/boe.fileio.cpp

@@ -24,6 +24,8 @@
 #include <sstream>
 #include <boost/algorithm/string.hpp>
 #include <fmt/format.h>
+#include "fileio/tarball.hpp"
+#include "gzstream.h"
 
 #define	DONE_BUTTON_ITEM	1
 
@@ -552,15 +554,33 @@ void try_auto_save(std::string reason) {
 	print_buf();
 }
 
-std::vector<std::string> extra_extensions = {".sav", ".txt", ".rtf", ".htm", ".html"};
-
 std::vector<fs::path> extra_files(fs::path scen_file) {
 	std::vector<fs::path> files;
 
 	std::string scen_extension = scen_file.extension().string();
 	std::transform(scen_extension.begin(), scen_extension.end(), scen_extension.begin(), tolower);
-	if(scen_extension != ".exs") return files;
+	if(scen_extension == ".boes"){
-
+		tarball pack;
+		igzstream gzin(scen_file.string().c_str());
+		pack.readFrom(gzin);
+		if(gzin.bad()) {
+			showError("There was an error checking for extra files");
+			return files;
+		}
+		for(auto file : pack){
+			fs::path path = file.filename;
+			if(path.parent_path() == "scenario/extra" && find(extra_extensions.begin(), extra_extensions.end(), path.extension()) != extra_extensions.end()){
+				extern fs::path tempDir;
+				// extract the extra file temporarily
+				std::istream& f = file.contents;
+				std::ofstream fout((tempDir / path.filename()).string(), std::ios::binary);
+				fout << f.rdbuf();
+				fout.close();
+				// Return that path
+				files.push_back(tempDir / path.filename());
+			}
+		}
+	}else if(scen_extension == ".exs"){
 		fs::path directory = scen_file.parent_path();
 
 		fs::recursive_directory_iterator file_iter(directory);
@@ -572,6 +592,7 @@ std::vector<fs::path> extra_files(fs::path scen_file) {
 				files.push_back(file);
 			}
 		}
+	}
 
 	return files;
 }

src/scenedit/scen.fileio.cpp

@@ -1236,6 +1236,21 @@ void save_scenario(bool rename, bool autosave) {
 		return;
 	}
 	
+	// Extra files! (Like readme.txt or a prefab party)
+	fs::path extraPath = tempDir/scenario_temp_dir_name/"extra";
+	if(fs::exists(extraPath) && fs::is_directory(extraPath)) {
+		fs::directory_iterator iter(extraPath);
+		for(; iter != fs::directory_iterator(); iter++) {
+			fs::path extra = iter->path();
+			if(find(extra_extensions.begin(), extra_extensions.end(), extra.extension()) != extra_extensions.end()){
+				std::ostream& extra_out = scen_file.newFile("scenario/extra/" + extra.filename().string());
+				std::ifstream fin(iter->path().string(), std::ios::binary);
+				extra_out << fin.rdbuf();
+				fin.close();
+			}
+		}
+	}
+
 	// Now, custom graphics.
 	if(spec_scen_g.is_old) {
 		spec_scen_g.convert_sheets();