I think just about every lucid dreamer has had difficulties summoning objects or people while lucid. I believe the problem is in the approach, trying to create something from nothing. Far easier to transmute something already in the dream into what you want to summon.

So how do we transmute dream objects? By taking advantage of archetypal associations. Everything is an archetype, and archetypes are nothing more than a series of associations or links. The trick is finding something in your dream that you can associate with what you want to manifest. This can be an obvious, direct association, or a series of abstract links. It doesn't have to be done with in one step, you can transmute something several times, each transmutation bringing you closer to your desired goal.

For example, in a recent lucid, I needed a female presence to balance something out, and I found myself standing next to myself holding a shotgun pointed at my double's feet. The path I decided to follow to manifest a woman was menstrual blood. So I shot my double in the feet, and the blood began to flow. But I conceptualized that blood as menstrual blood, and zoomed in on the bloody feet. When I pulled my focus back, my double was now a woman.

All summoning methods are just a variation of archetypal transmutation. Like the door trick for summoning people or teleporting yourself to a desired destination. Doors have to lead somewhere, that is the link, the association. But archetypes have many associations, and you have to choose the one you want to use before hand or you will end up with a random outcome.

Same goes with reaching into your pockets to summon something, or reaching to your hip for a gun or a sword. Pockets have a major association with carrying objects, that is their main purpose.

In order to properly transmute an archetype, you have to first make the association you want to use your main focus of attention. Zoom in on it visually so that it eclipses everything else in the dream. Then tweak your conceptualization of that element so that it is better suited to your purpose (Like how I changed bleeding feet to menstrual blood). The pull back your focused attention to take in more of the dream scene and the changes should have already taken place.

It's not always obvious associations either. When using this technique, you will often find yourself traveling down associative paths that are anything but obvious, connections you weren't even aware you made. But the paths are there none the less.

A word of warning, once you get the hang of this technique, it can completely destroy the narrative of your dreams.