Holding fluid, assuming healthy kidney function is primarily a result of water consumption and timing and secondary to the amount of carbs being injested and their timing.
Water retention is also largely related to sodium and potassium intake as well as physical activity.
Increased sodium causes the body to hold water to maintain correct osmotic balance and potassium helps the kidneys expel the water once sodium is reduced.
Doing strength training or vigorous physical activity beyond what you normally do will increase the water retention in the muscles as they heal themselves. This usually lasts just a couple of days and tends to be most pronounced the second day following the activity. It can easily add a pound or two to your weight depending on the level of activity and the strain on the muscles. If your muscles feel sore, you can bet you are retaining extra water.
A salty meal can also make you retain additional water the next day too as your body re-equilibrates to the sodium level ingested. Consume higher than usual sodium for a couple of days in a row and the water retention increases.
These are all part of the normal processes of the body and add to the noise of trying to track weight on a daily basis. More reason why long term moving averages are more revealing for progress toward weight loss goals.