The client is responsible for picking up non-vegetation items, such as toys, hoses, pet droppings, pieces of metal or wood, etc. Lawn mowers can cause damage to anything left in the yard, especially if they are in tall grass, unseen.
I would add that "If the objects are not picked up you can be charged for the time that it takes to remove the toys, metal, sticks and debris" (I wouldn’t pick up the crap)...I tell my customers we won’t use a string trimmer if there are several piles of poo in the yard.
The piece on late invoices that you removed should be included “If payment is not received 30 days after the invoice is dated you can be charged 8% on the cost of the bill” (just an example). I personally never add the charge but I will remind the customer that if they don’t pay that I can charge the late fee.
I personally prefer the “a la cart” menu for my business. Many of my customers that we mow for like to add a few services but not everything. It gives more freedom and people like choices; I rarely come across customers that want the full gambit. However, we all love those type of customers.
Contracts are tough to make clear and to cover all the angles. Every year I change something on my contract to make it easier to read or change because something happened. This year a homeowner put a herbicide down after my application killing the areas from their spot spray. So they blamed me and expected me to fix the lawn for free. So I am making it clearer in my contract for next year so that doesn’t happen again.
You are doing the right thing by creating this letter/contract. You one step ahead of where you were last year.