A guide for F2P version of Rocket league.Halo and Ion Boost are no longer easy to get via standard drops. There are now two optimal solutions to get this achievement and a few luck based ones:
Optimal solutions1. FREE solution. Find someone willing to lend you their item, equip it and win your match with it then give it back. This heavily depends on whether you know someone who has it or whether you can find someone on the internet (very difficult and time consuming - not recommended)
2. PAID solution. This can only be done if you have 300+ credits on your account (for the halo topper, ion boost is more expensive). You can either buy credits directly or if you are also going for the 200 item achievement and bought the rocket pass then you get credits every 10 levels until level 100 (900 credits total).
If you have the credits then visit
https://www.rl-trades.com/#h0=halo&pf=xbox. There you can see what people are offering and the credit amount they are requesting. This is being refreshed live and there are usually offers every few minutes. If you like some offer then click the "R-L.com" link to see the trader's Gamertag. Send them a message on xbox and trade away.
This way you can get the achievement within 10 minutes of trying. You can also try this in the TrueAchievements' "Item Trading" forum but it is not as active as the external one.
Important to note: For trading you need to have 2-factor authentication enabled for your EPIC account. Before you try this go and enable it on your EPIC account.
Luck-based solutions - I have over 90 hours played and never saw these two items so I would not rely on these solutions at all but you never know when you get lucky.
1. PAID solution. Wait for a blueprint drop. You get blueprints every few matches. If you have the necessary blueprint then navigate to Garage -> Manage Inventory -> Blueprints (second tab), find the blueprint you need, click

and

again to build the item. Note that this costs credits, usually a few hundred.
2. PAID solution. Wait for the item to be part of the daily sales in the item shop. Note that this would be extremely rare but you can get lucky.
3. FREE solution. These items can be sometimes part of the tournament chest rewards.
However this is currently not the case for Season 2. Seasons change every 3-4 months then you can check again by going to PLAY -> Tournament -> Rewards -> Highlight the reward "cup" and hit

.
Once you have either halo or ion boost (it
can be painted or certified):
1. Equip it
2. Go to PLAY -> Custom games -> Exhibition
3. Set Arena to "Starbase ARC"
4. Set Bot Difficulty to "No Bots"
5. Go to Mutator Settings and set "1 Goal" for the Max Score category
6. Score a goal and enjoy the pop