Ok this is my list of accessories that use on all of my strollers and i have lots so everything has to be universal.
First I have two mommy hooks they are black carabiners I have purchased generics b/c I like the other colors better but they didn't fit on the stroller. The mommy hooks make it easy at the end of the night to just unhook and leave all of the bags attached.
I have two valco baby universal cupholders easy to put on they hold my disney mug and they are adjustable. I did buy two munchkin cupholders they don't really work for me but they were awesome for my dd to use as a cupholder and they pop right off so again they are not in the way of folding the stroller, this works great b/c I have the mini that I can use the tray or belly bar w/ but my city classic doesn't take those accessories b/c it is older.
the bag use is the skip hop. I have the duo dash and the spark from target works great and its the cheapest you will find a skip hop that isnt used. If I am using a stroller that doesn't have a cupholder the skip hop works great.
Now I will admit that i say two of everything mostly b/c I have OCD and everything has to be in even numbers,lol. My dh hates it but then there are lots of times he is so grateful for it. Plus the extra cupholders work great for other family members who might need a place to put a drink. the mommy hooks I only used one this past trip. the trip before that I used two but I used one for the backpack that we had and the other was for bags that we accumulated during the day.
choosing between the belly bar and the snack tray I would go w/ the tray simply b/c your ds is older he will be getting in and out more the bar has to be completely removed where as the tray you simply undue one side and it rotates. the other thing that was nice about the mommy hooks is since my dd is disabled she stays in her stroller and if I didn't want all of our bulky bags hanging off in the pics it was super easy to pop the hooks off set them down and pick them up and hook them back as we were walking off and the same for buses. I know they have other stroller hooks but by far the mommy hooks are definitely more convenient. Sorry to go on for so long and this is just my opinion but it is what works for me if you have any questions feel free to ask away.
this is a pic from our trip in 2008 you can see the valcobaby cup holder and you see no baggage thanks to the mommy hooks,lol.
this was after we got back you can see how the cupholder is adjusted for the stroller when I need to fold it. you can also see how far the canopy comes down to the tray.
My dd was 5 at the time this pic was taken and she is a bit small for her age.
this is a pic of my skip hop spark and skip hop saddlebag attached.