Skip delivery step but add default shipping for order in spree. Add the following methods in your order_decorator and checkout_controller_decorator

checkout_controller_decorator.rb

def before_delivery
  if @order.needs_delivery?
    return if params[:order].present?

    packages = @order.shipments.map(&:to_package)
    @differentiator = Spree::Stock::Differentiator.new(@order, packages)
  else
    #we select the shipping for the user
    @order.select_default_shipping 
    @order.next #go to next step          
    #default logic for finalizing unless he can't select payment_method
    if @order.completed?
      session[:order_id] = nil
      flash.notice = Spree.t(:order_processed_successfully)
      flash[:commerce_tracking] = "nothing special"
      redirect_to completion_route
    else
      redirect_to checkout_state_path(@order.state)
    end
  end
end

order_decorator.rb

def needs_delivery?
  return false
end

def select_default_shipping
  #clone_billing_address #uncomment if user just types in one address
  create_proposed_shipments #creates the shippings
  shipments.first.update_amounts #uses the first shippings
  update_totals #updates the order
end