Allow user to upload file along with order

It looks to me like entirely different content types need to be created for each different product.

My most basic Node Checkout node type has more input fields than one image upload. Overall, my different products with Node Checkout associated node types all have very different sets of input fields, so I'm not feeling the urge to try to reuse one node type across multiple products.

I'm not sure if the architecture of Node Checkout would allow it. It would probably be a good idea to sit down and read through that module's code. Probably learn quite a bit...

Sounds like you may want to think of decoupling the uploading of images from your Node Checkout node types, and have a separate node type that allows users to load their own library of private images. Then, when products using Node Check are purchased, the node form is just browsing the user's private image library (and perhaps a store library too, for customers without an image to upload.) Your different products would still need a different content type for each browse the library node add operation, but they'd all be identical with only the help text changed as appropriate for the different products.

How comfortable are you in custom module development? I ask, because my Node Checkout based custom content types are all created in a content type implementing module, and I found it quite easy to tie things like product attributes to products and classes when working at that level (rather than with CCK and using the UI to create the custom content type.) Perhaps I'm not understanding what you're not understanding...

I hope you get that the Node Checkout custom content type is purely for information gathering on your side, and only binds to your product(s) through logic you implement in your own module, or through something like Conditional Actions, Rules or Triggers & Actions. I actually use the Conditional Actions method described by that blog post I gave above to finalize the purchase of custom products after the customer's credit card has been charged - however, in the Conditional Action triggered logic, I call a routine in my custom module that is doing more work than simply setting a variable and re-saving the node.

It sounds like your issue is a bit earlier in the transaction than at checkout. To get a better idea of the data you're working with, go to the edit page of one of the products in your store, take note of the node id shown in the browser's URL, and then in a new node (or other place you can execute some raw php within Drupal) execute this:

You may not have access to your php error log, so I use something like this to handle such situations rather than a direct call to error_log():

Anyway, this raw dump of a product node will show you that your product node has an array of 'attributes' objects, with each owning an array of 'options' objects. Depending upon the logic of what your attributes and options mean, you'll have multiple opportunities to insert logic into the browse-your-store-and-make-purchases activities of your customers. Conditional Actions has a wealth of places you can attach logic.

You may also want to look at the Cart Links module. I find it useful to describe 'pre-configured' product attribute/option combinations, and provide "buy now" links right in the product descriptions.

To answer your last question directly: I think so. When a product is purchased, you need that conditional action at checkout to tie your custom content type to the purchasing order and now-non-anonymous user. Afterward, your event registrant node will have a valid user id as well as a valid order id, and with that you can create logic to do whatever is necessary. Routines like uc_order_load($order_id) come in very handy when wanting to see specifics about an order...