If you are planning on having half days on Holidays, make sure the time is spelled out in the Parenting Plan (ex: Mom has children from XX to XX and Dad will have the children from XX to XX). Also, make sure that you put where the exchange will occur and at what time. My suggestion to you is that they happen in a public place in a half way point between both parent's house. Make this exchange place the place where all exchanges shall be made. Also, as far as special occasions you should write something to the effect that if there's a special occasion (weddings, funerals, etc) you are to have extra parenting time or parenting time shall be exchanged as long as you give a month's notice (well that doesn't work for funerals, but you know what I mean). As far as special occasions in your kids life (games, graduations, school plays, etc) write something to the effect that both parents are allowed to attend.
If you are agreeing to Joint Legal Custody (which I hope you are), make sure that it is outlined what decisions will be made jointly (ie: medical, religious, school, daycare, extra curricular activities, etc). Spell each of them out. I made the mistake of leaving it open ended and BM will not discuss anything with me stating that the only decisions that are made jointly are those of emergency.
If you are to have telephone access to the kids, write that in with days and times. In a clause write in that you are to have BM's current home address, home number, cell phone number, and work number for emergencies. You should each list three emergency contacts in the event that of an emergency where one parent can't find the other one. Write a clause that in the event of an emergency the other parent shall be notified as soon as possible but no later than an hour after the emergency. Write something about when you place a call to BM, how long after you call her she should return your calls (ex: all non-emergency phone calls shall be return no later than 24 hours after the request for a call back).
Check out some good sample parenting plans here
http://www.deltabravo.net/custody/articles.php (under parenting plan articles). A very important clause is to state how disagreements will be handled in the future if neither one of you can agree one an issue (for example, in NY you can go back to Mediation for free).
Good luck!