using (var ctx = new CustomerContext())
{
// 1. SPLIT the queries in multiple smaller queries
var customers = ctx.Customers
.Include(x => x.Orders.Select(y => y.Items.Select(z => z.Product))
.ToList();

var customers = ctx.Customers
.Include(x => x.Payments.Select(y => y.Items)
.ToList();

var customers = ctx.Customers
.Include(x => x.Shippings.Select(y => y.Items)
.ToList();

// 2. Done!
}