I left off with jointed veneer slices. I usually use two different methods to create wider sheets of veneer from narrower individual pieces. If the veneers are 1/8 in. or greater in thickness, I clamp them using very light clamps and weigh the sheet down afterwards to keep any of the veneer slices from buckling. This method works well for me and the photo illustrates how I do this. The other technique I use is to tape the two halves of veneer together and use the tape as the clamp. I place blue tape at regular intervals along the length of the veneers halves and make sure to do this on both sides of the veneers. This method works well with thin veneer slices as they cannot be easily clamped together any longer.
Another technique I sometimes use is to spring the joint, that is each side of the joint is so very slightly concave, there is a minuscule gap at the center of each of the slices. This technique only really works when clamping veneer halves together, veneers which are thicker than 1/8 in. The reasoning behind this is that when the center portion of the slices are clamped together, the ends of the slices are so much tighter there is little opportunity for the joint to open up. This is purely cautionary though, as once the veneers are laminated to the substrate there is little chance any of the joints will open up anyway.