I dont really think that there is an overall National Prescense simply for the fact that most are not totally Nation wide and will have areas of N-S-E-and W that will reflect certain ways of doing things. Not to say that there is not a Total overall projection through National HQs.
Each Chapter will have its different quirks so to speak!
Say while LXA has Its National Food Drive, each Chapters has certain Charity activities. LXA, We do a Hot-Tub-A-Thon and Western Week, some others do Watermelon Bust or Tetter-A-Thon.