Here is a quick way to build a Christmas Tree stand out of reclaimed pallet wood, 3 screws, and the bag from a box of wine.
Step 1: Get Your Pallet Wood, Drink Your Wine
Here's a good instructable on how to take apart a pallet quickly. Note that you should only use pallets that indicate "HT" for "Heat Treated" - meaning that it was not treated with nasty chemicals you don't want in your house.
For this stand you need 3 planks of 60 cm each. A EurPal is 120 cm, so that means you can cut two of the long top planks in half to get all you need.
Plastic bag from a box of wine
A box of wine contains about 20 glasses, so you should begin drinking in advance of this project - or invite a lot of friends to build stands with you.
Step 2: Draw Cut Lines on Your Wood
We're going to make a triangle with longer sides for stability. That means we need to cut two notches with 60 degree angles in each board. To make them easy to assemble, each board is notched differently. It helps to mark them.
Board 1: Top / Top
Board 2: Bottom / Bottom
Board 3: Top / Bottom
You can use any dimensions that will create enough space for your Christmas Tree Trunk in the inside - or make it a bit large so you can handle lots of different trunk sizes, with longer screws or bolts to hold the trunk. I recommend drawing lines at 5 cm, for the edge of the first notch, and 17 cm for the second. Note the 60 degree orientation of the planks, and their thickness, when drawing your lines.
Step 3: Cut Notches, Prepare Your Wine Bag
You want to cut your notches such that the wood fits together with a slight compression fit, but perfection is not required. Make the two cuts downward for each notch, and then knock the wood out with a hammer. Use a wood chisel to smooth out the bottom, and make sure the notch is 1/2 the length of the wood.
Assemble your triangle.
Remove your wine bag from the wine box and cut off the top edge and the valve.
Step 4: Insert Screws, Winebag, Tree
The winebag is your water reservoir. Stuff it down in your triangle with the open end upwards. Next, drill holes for long wood screws - just above their diameter. Start your screws about 2-3 cm from the top of each plank (This is important because they will make holes in your water bag, so they need to be placed high enough such that the bag can still contain enough water). Next, cut a small slice off the bottom of your trunk to help it draw water better. Insert your tree, position it vertically and then drive your screws or bolts into the trunk. It may not be necessary to screw them all the way in - just enough to hold strongly enough to keep the tree standing vertically.
Next, pour water next to the trunk until it fills the bag - but only up to where the screws have penetrated it. Any further and it will leak out of the holes made by the screws.