To make sandwiches ahead of time without getting soggy, toast the bread to create a moisture barrier or even use ingredients that have a lower moisture content and place any wet ingredients like tomatoes in the center of the sandwich.
Also add any condiments separately to the sandwiches to apply later and wrap the sandwich in paper or parchment paper tightly and then place the wrapped sandwiches in a container for a second layer of protection.
To keep your sandwiches from getting soggy in a lunch box, or any other time use a moisture barrier with cheese or even a layer of butter/mayo.
Also keep any wet ingredients like tomatoes or pickles in the center of your sandwiches and use some parchment paper or sturdy wrap for the exterior of the sandwich.
And pack any dressings for the sandwich separately from the sandwiches in the lunch box and store your finished sandwich in a hard sided container to prevent crusting.
Toasting the bread even lightly can also help keep the sandwiches from getting soggy in the lunch box.
Using cheese and or lettuce can also absorb moisture and prevent the sandwich from getting soggy or even spread a thin layer of butter, mayonnaise or other condiments directly onto the bread, which creates a good barrier against moisture from the other ingredients.
Mayo will sometimes make a sandwich soggy overnight, as the moisture and other ingredients in the mayo can soak into the bread.
Although you can use a thin layer of oil based mayo on the bread which can act as a moisture barrier and protect the bread from wetter ingredients.
You can also toast the bread, pat the produce dry and build a barrier with a dry ingredient between the wet fillings and the bread to prevent it from going soggy or assemble the mayo sandwich just before eating or wrap it in plastic wrap before refrigerating it.
You can make egg mayo sandwiches the night before or even other types of mayo sandwiches the night before.
Although when making egg mayo sandwiches or other sandwiches with mayo the night before you should wrap the egg mayo sandwiches well and store the egg mayo sandwiches in the refrigerator overnight to prevent the bread from drying out and to also maintain the freshness of the egg mayo sandwiches.
The egg mayo sandwiches made the night before are best eaten within a day to maintain their quality and avoid the egg mayo sandwiches going soggy.
When making egg mayo sandwiches the night before it's best to prepare the egg mayo filling and then store it separately in the refrigerator.
Then for the freshest egg mayo sandwich, it's best to assemble the egg mayo sandwich the next day but prepare the egg mayo sandwich ingredients the night before.
If you do need to make the egg mayo sandwich the night before you can do so but you should also wrap the egg mayo sandwich tightly in plastic wrap and or place it in an airtight container.
Store the wrapped egg may sandwich in the refrigerator overnight.
And if time allows you can take the egg mayo sandwich out of the fridge up to 30 to 60 minutes before you eat or serve them to allow the bread to become room temperature warm.
And to help prevent the bread of the egg mayo sandwich from getting soggy from the mayo, you can also spread a thin layer of butter on the bread before you add the egg mixture.
Just avoid overfilling the egg mayo sandwich with the egg mixture, as this can also result in the egg mayo sandwich becoming soggy.
And if possible you should use high quality mayonnaise and fresh eggs that will also improve the flavor and texture of the egg mayo sandwich.