First is the frequently bought together app. This app upsells products to customers, which will lead to your orders being higher amounts
Second we have the currency converter, lots of your customers will be overseas so you will need an app which converts the currency for the customer.
And lastly, any email and sms marketing tool like klaviyo or yotpo bump, which will help you send campaigns when you drop/restock products and also send an email to customers who have abandoned checkout.