namespace LightSwitchApplication
{
    public partial class RegisterInkasBag
    {
        partial void SequenceNumber_Compute(ref int result)
        {
             //Присваиваем номер по порядку
            IEnumerable<int> num = this.JournalInkassBag.RegisterInkasBags.Select(n=>n.SequenceNumber=n.SequenceNumber+1);
            foreach(var seqnum in num)
           {
              result = seqnum;
           }
        
        }
    }
}

 partial void SequenceNumber_Compute(ref int result)
        {
             //Присваиваем номер по порядку
RegisterInkasBag [] num=this.JournalInkassBag.RegisterInkasBags.ToArray();
            IEnumerable<int> query = num.Select((n,i)=>i);
            foreach(var seqnum in query)
           {

              result = seqnum;
           }
        
        }

 IEnumerable<int> query = num.Select((n,i)=>i,[SIZE=3]?[/SIZE]);

Private Sub Recount()
Dim nom As Integer 'номер сумки по порядку
nom = nom + 1
Label1.Text = nom
End Sub

namespace LightSwitchApplication
{
    public partial class RegisterInkasBag
    {
        partial void SequenceNumber_Compute(ref int result)
        {
           result = this.JournalInkassBag.RegisterInkasBags.Max(n=>n.SequenceNumber).FirstOrDefault(0) + 1;
        }
    }
}

private int _number = 0;
partial void SequenceNumber_Compute(ref int result)
{
    _number++;
    result = _number;
}

var items = list.Select((a, num) => new { num = num + 1, value = a });