Unfortunately, you can't get more Repair Kits than the starting 3 the game gives you at the start of every Mission. You can use a Supply point to restore your health and get the Repair Kits back if you used them earlier on, but there's no way to upgrade the feature to hold more than 3 at any one time. The only thing you can do is unlock an OS Tuning Upgrade to make them more effective when used. For more information, please refer to our Best OS Tuning Upgrades guide.