You can make button extenders to expand the waistband of too-tight trousers or shirt collars by up to 1 1/2 inches. Look for fabric matching the garment fabric if the extender is for a shirt collar. Use fabric one shade darker for trousers waistbands, so the extender will blend into the background. Make sure the buttons are also the same size as the garment buttons, by measuring the original button and then using a matching button.
Position the fabric rectangles so they are lined up, with the right sides together. Place the interfacing rectangle on top of the rectangles, with the interfacing's edges lined up with the fabric's edges.
Place a pin in one 2-inch-wide end as a reminder to leave that end open when sewing. It does not matter which end you choose, as long as it is one of the 2-inch-wide ends.
Sew around the three unpinned edges with the sewing machine, making a 1/4-inch seam allowance. Use a straight stitch for this seam.
Clip the corners with the scissors, making diagonal cuts that do not cut through the stitching. Turn the fabric rectangle right side out, and flatten the seams by wiggling the fabric back and forth under your fingertips.
Fold the open end in 1/4 inch, and work with the fabric until the seams are flat. Top-stitch 1/8 inch in, all the way around the rectangle to finish all the folded edges.
Set the buttonhole stitch on the sewing machine, and position the presser foot so the machine will sew the buttonhole 1/2 inch from the extender end, and running across the short edge of the extender. It does not matter which short edge you choose, either one will work. Sew the buttonhole, and then use the scissors to make a slit in the centre of the buttonhole stitching.
Thread the hand sewing needle, making sure to knot the thread ends. Position the needle 1/2 inch from the extender end that does not have a buttonhole. Poke the needle through the fabric, move the needle over 1/8 inch, and then poke it back through the fabric. Slide the button onto the needle and against the fabric. The button will cover the knotted thread end.
Poke the needle point into the fabric as close as possible to the knot, and then push the needle through the fabric. Draw the thread tight by pulling gently. Repeat the stitching to attach the button, pulling the thread through the fabric and button at least eight times, and then secure the thread by making at least three tiny stitches under the edge of the button.
To use the extender, fasten your garment's original button through the extender's buttonhole. Then, fasten the extender's button in the garment's original buttonhole. If you do not need a full inch and a half, you can move the button in as much as needed, before sewing it on, to adjust the size of the extender.