Some travel insurance policies will include a certain number of activities for free. Some will only cover them on payment of an additional premium and some will totally exclude them. 24/7 travel insurance automatically includes over 100 activities with all of their policies, from abseiling to yoga and include things like swimming with dolphins and bungee jumping.
You need to remember that if you are injured whilst taking part in a sport or activity that is not covered under the policy or that you did not make your travel insurance company aware of, they may not pay out on a claim. That can include your medical expenses and repatriation home which can be very costly.
The 24/7 Single Trip travel insurance policy has 7 activity packs to choose from in addition to the free one. Do remember there may be an additional premium depending on the level of activity.
The normal add on package you find on most single trip policies is for Winter Sports and includes skiing and snowboarding activities.
Please remember to read your policy documents thoroughly before travelling to avoid confusion and taking part in something that may possible void your cover.