No matter what the contents of your lunch are, you can rest assured! I found a product called "Assembled Cutlery Set" at Daiso and bought it.
This set is a product that contains three disassembled chopsticks, a spoon, and a fork in one case. The blue stick is the "handle", and you can transform it into the cutlery you want to use by replacing the tip.
Insert two white sticks into chopsticks
A set of fork and spoon is also available in no time
It may be individual difference of the product, but I got the impression that the chopsticks could be attached smoothly, while the fork and spoon were a little difficult to attach and remove. Therefore, it may be recommended for people who say, "I usually use chopsticks, but sometimes I want to use a fork or spoon," rather than those who often use forks and spoons.
Similar products are available at stores other than 100-yen shops. There are various designs, so if you are interested, why not check it out?