To fulfill your requirement may be returns may solve it.

  function revealWinners() public returns (uint) {
        for (uint id = 0; id <3; id++) {
            Item storage currentItem=items[id];
            if(currentItem.itemTokens.length != 0) {
                uint randomIndex = (block.number /
                currentItem.itemTokens.length)% currentItem.itemTokens.length;
                uint winnerId = currentItem.itemTokens[randomIndex];
                return winnerId;
        }
    }
 }

To fulfill your requirement may be returns may solve it.

  function revealWinners() public returns (uint) {
        for (uint id = 0; id <3; id++) {
            Item storage currentItem=items[id];
            if(currentItem.itemTokens.length != 0) {
                uint randomIndex = (block.number /
                currentItem.itemTokens.length)% currentItem.itemTokens.length;
                uint winnerId = currentItem.itemTokens[randomIndex];
                return winnerId;
        }
    }
 }

update:

If you want to return any value from the function then you have to use return keyword as other programming language do . As you see in the function

function revealWinners() public returns (uint){

you have to use returns(data_type_Or_datatype_with_name) in the function. so the function have to be like this:-

function functio_Name(agr1,agr2,..) returns (ret_arg1,ret_arg2,..){
//logic here
return(ret_arg1,ret_arg2,..)
}