Get custom post fields from multiple metaboxes

If I understand your question correctly, you would like to get all metadata for “products” across all posts. In other words, multiple posts have metadata with key “products” and you want to get those values. If this is correct, you should use get_post_custom_values, which is well documented in the codex: http://codex.wordpress.org/Function_Reference/get_post_custom_values.

As a side note, are you using the Meta Box API for your meta boxes. If not, you definitely should. I’d recommend taking a look at these two articles to get started with meta boxes:

http://codex.wordpress.org/Function_Reference/add_meta_box

http://www.wproots.com/complex-meta-boxes-in-wordpress/ (In the interest of full disclosure, I wrote this and it is completely on topic)