Yes, there is a shopping cart feature. You can switch it on in Site Settings. Once switched on, your clients will need to check out to finish the reservation and will be able to put multiple items into their shopping cart.
The way this works is that the first reservation is done normally, that is, the reservation form is filled out and then the customer is taken to a page controlled by a template (you can also edit it in site settings / templates). This template normally displays the contents of the shopping cart, the checkout buttons and suggestions of other items which can be reserved. This suggestion is implemented in form of a search. The search can find items available in the exact same period as the first item reserved (e.g. January 1-7) or you can use the flexible search which will find items which can be reserved for any duration within the original dates (e.g. on January 2nd). This type of search is great if you want to offer e.g. rooms as well as tours. This way, before checking out, your customers can see a list of tours available within the reserved dates.
Another way to let your customers make a reservation for multiple resources are
packages. Here the advantage is that you can set a special price when multiple items are reserved together. The package must be predefined by the administrator first (specific items will make up a package), so it's a different solution than the shopping cart. See
Q232 for more info on packages.