in terms of revenue synergies you could think of the following:
- Selling additional products to the same customers
- Selling the same products to additional customers (new geographies, new market segments new industries, etc.)
In terms of cost synergies, think of all costs that typically occur. One strategy to make sure you don't forget anything can be to draw the value chain and list the respective costs for each item in the value chain.
I hope this helps.