Let me explain how I handle trips (the same works for projects though):
As I have many trip notes, I have a tag called #trip and a collection ✱ Trips, which shows all notes tagged with #trip. I use trip notes for planning, storing receipts of booked tours as well as keeping a travel journal for that trip.
So on my "2015 Summer Holiday" note which is tagged with both #trip as well as #2015SummerHoliday I have sections (Headings) for Journal, Itinerary, and Planning. In the Planning section I might have Sub-headings for Hotels, Tours, etc. with links to external websites. But I also create new notes that include receipts or more information for a specific aspect of that trip. These notes don't get the tag #trip, they only get the tag #2015SummerHoliday. And as good practice, they all have a link to the main "2015 Summer Holiday" note.
So in your ✱ Trips collection, you can easily find your trip note for the 2015 Summer Holiday, and within it you'll find all linked resources.