I think other than a spice rack - which you certainly can do "after market" - I would wait. Unless you want some sort of specific custom pullout or lazy susan type option...which still can be added after. And I would add the insert for the trays/cutting boards as a built in (if you wanted such a thing)
I'm still arranging and rearranging 2 months after my remodel. I have bought things for drawers at TJ Maxx (great prices!) and Bed Bath and Beyond. My cabinet maker *did* make me several drawer inserts for my cutlery and utensils, but mine were included as part of his price.
Some things fit better...some it's nice to have them removable for ease of cleaning. All my inserts lift out so I can clean out my drawer and replace my drawer liners. Also my extra utensil dividers (store bought) all lift out so I can clean in case of a spill, etc. Iwould make a list of your wants, needs, gather photos and ideas...look around at Ikea, container store, BBB, etc and see what is out there. A lot of the add ons from the kitchen places can really add up fast, I think.

I found custom made inserts from Woodhollow were a much better value they're made to measure so they fit perfectly. The ones that come with the cabinets are very nice and if in the budget then certainly go for it but if they're too pricy Woodhollow is an excellent alternative.

Ooh, good to know about Woodhollow, I'll check them out.

The only insert I got from my cabinet company was the trash pullout because I liked it and it wasn't too expensive compared to after-market versions. In my last house I used a Rev-a-Shelf version and I liked that too. I purchased both the telescoping towel bar and the condiment pull out (both Hafele) myself and had my contractor install them, because they were much less expensive than the cabinet co's version, and I liked them better as well. For spices I got IKEA holders that I love (but even then, I waited to see whether I would store the spices in a drawer or in a cabinet).

i got the 2 tier cutlery tray and it was well worth it! you can't get the 2 layer kind aftermarket,

Ah yes, I don't even think of the trash pullout as an extra, that was definitely on our wish list. I'm not so sure how I feel about the double tier cutlery organizer -- my parents have one and it's annoying because you can't fit very much in one layer and it will never close.

@christina222_gw, is the Woodhollow you mentioned the same as Woodhollow Cabinets? I can't quite figure out how you would order from them not through a dealer.

Woodhollow inserts are from the cabinet company. They sell the inserts to consumers on eBay. My inserts shipped yesterday; should arrive tomorrow. I'm giddy!

Awesome, great to know. Let me know how you like your inserts -- we have a while to go before I'll be at that point (looking *so* forward to three kitchenless months with two young kids).

Woodhollow does have a two tiered cutlery insert.