I'm using latex house paint in matte black, chocolate brown, and light grey for the highlights.
Our first step is to paint in all the nooks and crannies in the foam.
Mix the paint about 50/50 with water to thin it. This will carry the paint way down into the crevices and darken the deep places, and will keep the polycarbonate underneath relatively paint-free so the light will still shine through. Use a paintbrush to work it in.
I alternated brown and black paint for this part, to give more depth of color to my staff.
(For my previous prototype I used just black and no brown, and the staff came out looking more like wood that had been in the fire for a while, all ashen and burnt, which is also a very cool effect.)
Don't worry too much about getting paint on the water bottle. The thinned latex paint doesn't care to stick to the plastic too much, and once it dries, we'll clean it up a bit using 99% alcohol.
You can stop here, or create more of an oak-tree look by adding a light grey highlight.
Let the base coat dry, then use your paintbrush and a light grey latex paint (not thinned) to brush very lightly across the top of your staff. The paint will hit just the peaks and highlight all the lovely texture created by the foam.
Use a utility knife to carefully cut a flap in your water bottle so you can access the inside where the bottle attaches to the tube. Make the cuts beneath the foam to hide them. Don't cut the window out entirely - just cut enough that you can peel back a flap of plastic and reach the inside.
Lay out your LED strip next to your staff, with the top of the lights next to where the bottle attaches. Measure and cut the lights carefully across the copper pads at the bottom of your staff. Seal up the end using hot glue and clear heat shrink.
Count how many LEDs you have in your strip, so you can use that number in your code.
Feed the LED strip down inside the polycarbonate tube from the top until all the lights are inside the staff. Then, slip the battery into the top of the tube above the lights. It should fit fairly snugly -- if it's really loose, add some tape around it so it doesn't shake around.
Find a good location for the speaker. It'll sound best if it's up inside the water bottle, but it's nice if it's hidden from view behind some expanding foam. Hot glue it into place.
Cut a small hole in the side of the bottle for the switch to come through. Thread the switch and wires through the hole, but leave it dangling loose for now -- we'll secure it down a bit later.
I used some black plastic tape to secure the NeoPixel ring to the back of the FeatherWing assembly. I wanted a tight, small package but also needed to avoid any potential short circuiting due to the parts bumping against each other. Adding the tape in between was a good solution.
I nestled the FeatherWing assembly and NeoPixel ring carefully into the base of the staff head, so the ring lights shine up into the bottle and the USB port is accessible through my window flap. The board is oriented flat with the floor when the staff is upright. Once I was happy with the placement, and was sure everything was working, I hot-glued the board and ring in place.
This last bit was pretty tricky, and every staff will be different. You can always add more expanding foam if you end up cutting away too much! This material is really forgiving.
Finally, I threaded the on/off switch around until I found a nice hollow for it to nestle into. As a finishing touch, I used silicone glue to glue a jewel above the switch (being careful not to get any glue IN the switch). Silicone glue is rubbery when it dries, so this allows the switch to be activated when I press on the jewel.
Finally, I added a little bit of crumpled iridescent cellophane to the inside of the water bottle, in order to catch the light and give a magical sheen to the NeoPixel colors.